I'm not known around the Internet as the world's biggest A.J. Burnett fan. During last Wednesday's BP roundtable, I even dusted off an old Simpson's riff: "I'm a well-wisher in that I wish him no specific harm." Now, to set the record straight, any voodoo dolls I may have referenced over the past decade or so for any player exist only in my breathlessly hyperbolic narratives, and I would never actually wish injury on a ballplayer, particularly not such an injury as befell Burnett later that day. The recent trade that sent the enigmatic righty from the Yankees to the Pirates mandates that he practice his hitting and bunting, and unfortunately, a less-than-stellar bit of work on the latter sent a ball into his own face, fracturing his right orbital and necessitating surgery. Fortunately, it does not sound as though he suffered a detached retina, which could have threatened his career.

Even limiting myself to Yankees past and present, it's not hard to come up with a short list of pitchers injured in the line of carrying out offensive responsibilities for which they were increasingly ill-suited. Last year, Dustin Moseley, then in the midst of a career resurgence with the Padres, dislocated his non-throwing shoulder twice while swinging a bat and was forced to undergo season-ending surgery in August to repair tears in his labrum and shoulder capsule. Randy Johnson strained his shoulder swinging a bat for the Giants in 2009, missed two-and-a-half months, and never started another game. Chien-Ming Wang's downward spiral began with a torn tendon in his foot suffered while running the bases in 2008. Bartolo Colon hurt his lower back hacking away in 2008, one more injury during a stretch of them that put his career on the ropes.

Moving past the pinstripes of yore, the Palooka Formerly Known as Fausto Carmona strained his quad while running the bases last year and needed a DL stint. Boston's Clay Buchholz lost more than three weeks to a hamstring strain suffered running during his first major-league plate appearance in 2010. Teammate Josh Beckett hurt his back in batting practice that year as well, and made just one start in a two-and-a-half month span. The Blue Jays' Scott Downs injured a ligament in his toe coming out of the batter's box in 2009, and soon needed ligament replacement surgery. Jake Peavy injured his ankle rounding the bases in May 2009 and hasn't pitched a full season since. Perhaps tiptoeing past direct causality, Mark Prior violently collided with Marcus Giles while running the bases in 2003 and landed on his throwing shoulder. While he remained in the game, he missed his next four starts while on the DL with a sore shoulder, and some have attributed the injury to the beginning of Prior’s own descent into arm woes.

While these anecdotal points don't themselves constitute an epidemic of injuries, it's fair to ask again, "Why are we still letting pitchers hit?" The designated hitter rule has been on the books in the American League since 1973, has been used in the World Series since 1976 (in even-numbered years through 1984, and all games in AL parks since 1986), and in AL parks during regular-season interleague play since 1997. Baseball hasn't become less popular during that timeframe, and the world hasn't stopped spinning on its axis. Meanwhile, pitchers have only gotten worse as hitters. In 1954, the rolling five-year True Average for pitchers was .176. In 1972, the last year before the DH went into effect, it was .153. Last year it was .145, just up from its all-time low of .143, via a .141/.175/.183 line. Less of this, please.

Some may feel that the designated hitter has eliminated a certain class of strategic options in such games, but how much affection should we have for sacrifice bunts and the underperformance of pinch-hitters (rolling five-year TAvs ranging between .231-.240 since 1988)? How are those near-automatic outs worth exposing pitchers to additional risks for which they're increasingly ill-suited? The mound is dangerous enough as it is when it comes to throwing and fielding, and losing talented pitchers to preventable injuries elsewhere on the diamond is a particularly awful way to go. Furthermore, teams and managers could arguably gain more out of their pitchers if their removal weren't so circumscribed by the rhythm of the batting order. Perhaps the uniformity of the DH would help roll back the tide of La Russaism to reduce the size of pitching staffs, avoiding the tedious burning of extra pinch-hitters and lefty specialists.

As a lifelong NL-first fan, I'll admit that arguing on behalf of the designated hitter's adoption across both leagues wasn't something I planned on doing when I set out along my journey across the defensive spectrum, but it does provide a conveniently topical opener as we peer into an enduring mystery. Recall that the spectrum (first defined by Bill James) runs DH-1B-LF-RF-3B-CF-2B-SS-C, with the positions to the left, which require the least defensive responsibility, open to the widest pool of hitters and therefore likely to be the most productive. Yet when we examine annual True Averages by position, we find that designated hitters—who have absolutely no defensive responsibility—haven't been living up to their end of the bargain. Here's a rerun of the graph showing the annual TAvs by position:

Here's a closer look at the left portion of the spectrum using five-year rolling TAvs:

As noted in the opening article to this series, designated hitters have consistently underperformed relative to their far left position on the spectrum. They've never—not once in 39 seasons—actually ranked as the most productive position according to True Average, and have ranked second only five times in that span. Only in 1983, when they had an edge of less than one-tenth of a point (.27556 to .27547), did they actually overtake first base; both took a back seat to left fielders (.2766) that season. A great deal of the time, DHs haven't even been able to outhit corner outfielders or first basemen; their average annual ranking since the advent of the rule is 4.15, and they've ranked fourth seven times in the past 11 years. To be fair, they've also ranked second three times in that span, in 2006, 2007, and 2009, and last year ranked third at .276.

Looking back at either of the above graphs, that recent performance—which includes seven straight third-place rankings from 1994-2000—is actually significantly better than the first two decades or so of the position's existence. From 1973 through 1993, DHs hit for a .267 True Average, and held an average 4.95 ranking, finishing sixth nine times in 21 years, and seventh once (1977)—behind catchers, even, and ahead of only middle infielders—while ranking second only twice. They never actually fell below the league average of .260, because back in the shag-carpeted ‘70s, the gap between shortstops and the rest of the pack was so huge. However, even during the mass-market era of James' annual Baseball Abstracts (1982-1988) when the concept of the defensive spectrum was first widely propagated, teams struggled to find bats effective enough to fill the position. Perhaps their shortfall in a measure (True Average, née Equivalent Average) that was still more than a decade away from being invented is excusable. Hell, James himself didn't pontificate about the importance of on-base percentage nearly as much as his latter-day sabermetric followers have given him credit for.

A quick scan of the most popular DHs from 1973-1993 shows a tolerance for true mediocrity. Of the 100 with the most games at the position, 23 had OPSes of 700 or lower, and 40 were at 722—the AL's average OPS over that span—or lower. Forty-three of them had OBPs of .328 (AL's long-term average over that span) or below, including many an aging star: Tony Oliva (.328), Hank Aaron (.327), Willie Horton (.321), Tommy Davis (.321), Harmon Killebrew (.313), Ted Simmons (.311), Dave Parker (.306), Cecil Cooper (.298), Carlton Fisk (.291). Thirty-six had slugging percentages of .394 (again, the AL's long-term average) or below, including Simmons (.392), Al Kaline (.390), Fisk (.387), Oliva (.386), Ken Singleton (.385), Aaron (.367), Davis (.365), Killebrew (.355), Alex Johnson (.353). Reggie Jackson hit just .227/.332/.407 in 2,563 career PA as a DH, while Carl Yastrzemski hit .264/.350/.411 in 1,712 PA; neither would have gotten a bronze plaque in Cooperstown for that kind of work.

Since 1993, DH performance has actually been on the uptick, a counterintuitive finding given that the majors have expanded twice during that span—if not creating more AL teams (there have been 14 since 1977, with the Rays replacing the Brewers in 1998), then creating more major-league jobs where mashers who might be less competent fielders might take refuge. Then again, the player pool has expanded, with more Latin American and Asian players in recent years (Hideki Matsui says "Konnichiwa"). After hitting for that .267 TAv from 1973-1993, DHs have hit at a .274 clip since.

If we instead move the cutoff to a more logical point—before and after the advent of interleague play in 1997—the difference narrows by about two points (one of which is lost in the rounding), to .268-.274. Last year it was .276, the position's highest mark since 2007. That was up from .268 the year before, the lowest mark since 1993, when it was .264, creating a perception that I believe carried over into last year despite the significant improvement. Adam Dunn alone (.176/.305/.314 as a DH) was a walking confirmation bias of the position's perceived decline—walking back to the dugout after striking out again.

The split between pre-interleague and interleague eras is restored to seven points (.268-.275) if you exclude NL DHs, who have hit for just a .258 TAv—slightly below what a league-average hitter would do—since interleague began, albeit in a sample size that's 5.7 percent the size of their AL counterparts. Note how closely the MLB combined line hews to the AL line, and how the extreme spikes on the NL side only cause a maximum of three points' deviation in either direction:

The gap between AL and NL DH performance raises the question of whether the junior circuit's advantage comes from generally having a roster spot dedicated to the position, while the senior circuit scrambles for the next available bench guy to fill the role, or if there's something else at work. Here's how the two leagues' batters have performed when not DHing or pinch-hitting (which I've excluded from the sample because of their notoriously mediocre performances) in the same season:

Surprisingly, it's the NL with the stronger caliber of hitters, something that's been the case in all but the first two years of interleague play; over the course of the 1997-2011 span, the margin is a sizable seven points, .281-.274. So the AL DHs hit one point higher in their DH role than in non-DH, non-PH roles, but the NL hitters fell off by a whopping 23 points. What this suggests is that rather than promoting a bench player to the role—after all, there aren't a lot of .280ish TAv hitters riding pine—teams tend to move some of their most productive players to the DH spot for interleague play, either for a general breather or as a means of staying in the lineup when at less than 100 percent. Some combination of minor injury and the pinch-hit disadvantage might explain why those NL hitters still struggle so. It's also worth noting that an hitter may be taking those good hitters' spots in the field, somewhat balancing things out somewhat, but I didn't attempt to confirm that theory.

One of the oft-repeated theories about the offensive shortcomings of DHs as a class—and I'm sure I've been guilty of this somewhere—is the perceived decline in the number of full-time or near-full-time DHs, the David Ortizes and the Travis Hafners. At the 500-plate appearance level, there's a wee bit of truth to that, but we're dealing with a fairly small number of players. At the 300- or 400-PA level, it just ain't so:

The number of DHs at the 300- or 400-PA levels has actually been trending upward since 2004. Which isn't to say that their performance has:

Here we have a bit more of a clue as to what's been going on in recent years: The performances of the most-used DHs have been declining, and in a small population of players, that makes a difference. Note that the 2005 spike of the 500-PA DHs is the composite performance of Ortiz and Hafner—and nobody else, so of course it's a long way down from those heights, which were actually a bit lower than the two sluggers' 2006 marks (.338 for Ortiz, .349 for Hafner). Note that at whatever cutoff point we draw for regulars, their performances exceed those of the DH population as a whole by at least 20 points from 1999-2007, but that they've converged much closer since—not coincidentally, since Ortiz and Hafner themselves have aged and become vulnerable to injuries. The former fell from .343 in 2007 to .293 in 2008 and then to .273 in 2009, his low as a Red Sock. The latter fell from .349 in 2006 to .293 in 2007, and then was limited to 233 PA and a .229 TAv by shoulder woes in 2008. In the three years since, he has exceeded 400 PA just once, though his TAvs have rebounded into the .290-.305 range. As a matter of fact, the DH population is an aging one:

Again note the lack of an impact on the overall average by the NL DHs. Furthermore, note that while the average age of all hitters (weighted by plate appearances) has been relatively stable, it's been trending slightly downward for the past seven years while the average DH age has been increasing, to the point where the gap between the two groups has nearly tripled, from 1.3 years in 2005 to 3.8 years in 2011, with the five-year rolling averages increasing from just under two years to over three. Last year, the average DH age reached 32.5, its highest since it was 32.6 in 1998. With the likes of Matsui (462 PA as a DH in his age-36 season), Johnny Damon (596 in his age-37 season), Vladimir Guerrero (582 in his age-36 season) all currently jobless, and with few DH spots apparently vacant, it could be that we're in for a correction this year.

It could also be that we're approaching a tipping point. The 2013 realignment will send the Astros to the AL and necessitate at least one interleague series at any point on the schedule due to the odd number of teams in each league. MLB hasn't finalized the actual number of interleague games for each team; at one point it was rumored to be 30, and it may yet be, though current signs point to 15-18 as in recent years. Familiarity may breed contempt, but the prolonged exposure to the DH in place of lame pitcher swings (and lame pitchers) may push the conversation toward adoption of the rule in the NL. It's logical step given the other wide-reaching, tradition-challenging changes of the Selig era such as the wild card and interleague itself, and you can bet that the Players Association wouldn't object to the possibility of another 15 jobs at above-average salaries. A.J. Burnett might not object, either, and after poring over the data for the past couple of weeks, neither would I.