For someone who tends to watch more American League affairs than Senior Circuit contests, interleague play serves as an annual reminder of just how superlatively talented major-league players are. When every player on the field is doing the job for which he’s been selected, the game can appear deceptively easy, even at its highest level. The man on the mound is always among the best in the world at harassing hitters, but the bloke in the batter’s box is usually similarly skilled at making the moundsman’s life miserable. As a result, neither party typically appears especially outmatched, unless the party of the second part is Tony Pena Jr., in which case he’s about to trade places anyway. Only if you or I were to don a major-league uni might we catch a glimpse of the true talent gap, but an MLB cameo for a mere mortal is less likely to transpire than the sight of a big-leaguer suiting up for a beer-league softball game.

Even more so than Yuniesky Betancourt, pitchers at the plate offer our best chance of appreciating the skill level that graces the game to which we’ve devoted our attentions. Most major-league hurlers were good hitters at some level of competition, but watching one step into a big-league batters’ box is akin to spotting that guy who abandoned his musical career after bringing down the house at your high school recorder recital sitting down on stage with the New York Philharmonic.    

Just how much worse at hitting are the players who’ve made it to the majors on pitching prowess alone? Most of us could come up with a reasonable estimate for the present day, but we might not be aware of how drastically the answer to that question has changed over time, and continues to differ depending on context. By comparing historical offensive production for pitchers to offensive production for the league as a whole, we can visualize the changes. Here’s a graph of the differential between league-average OPS and league-average OPS for pitchers (in their offensive capacities) over time:

Since the institution of the DH, AL pitchers have generally been a good deal worse than their respective league averages, relative to their NL counterparts. This makes sense, intuitively. We know that practice doesn’t always make perfect, but it usually makes improved, and NL pitchers are getting far more of it than their AL counterparts. Nate Silver found that pitchers don’t peak offensively in their mid-to-late 20s, as do players of other positions. Instead, they grow gradually worse, since their roles allow them scant chance to (as Nate put it) “compensate for the decline in raw athletic skill” by learning from experience. We’re looking at single seasons here, not an individual’s decline over time, but the same effect is likely at work—the pitchers who rarely get to hit become worse hitters as a consequence.

However, this graph is somewhat deceptive; since the post-DH, pre-interleague era is omitted from the trend line, we’re missing a good deal of data on NL pitchers’ performance. Here’s another version, with the full trajectory for the NLers restored:

While NL pitchers have declined less than AL pitchers, relative to their league’s average offensive performance, they have experienced a drop-off, nonetheless. Why should that be? After all, NL pitchers still dig in regularly against opposing starters. My theory has to do with increasing specialization. As the talent pool from which MLB players are drawn has grown, the elite performers who make the majors have simply gotten more talented at whatever it is they were brought to the majors to do. On the whole, hitters are better at hitting than they used to be (and pitchers are better at pitching) meaning that there’s a greater separation between the average major-league hitter and the average major-league pitcher who just happens to hit. However, there could be other factors at work; perhaps the decline is the result of less offensive exposure in the minors (minor-league pitchers hit only for NL affiliates at Double-A and Triple-A), or an annual influx of migrant workers from the AL. If you have any other theories, feel free to leave them in the comments.

We’ve compared the leagues’ pitchers graphically in terms of how they stack up to the overall offensive production, but we haven’t yet pitted them against each other directly. The following graph displays the difference in average OPS between NL and AL pitchers over time:

During the pre-DH days, the leagues were neck-and neck. From 1997-2009, AL pitchers averaged only 310 plate appearance per season, so their batting lines were subject to a fair amount of fluctuation, but the trend is clearly one of increased offensive output by the NL. We can also represent this information in tabular form. Here are the average NL-AL differentials for the pre-DH and post-interleague periods, weighted by plate appearances:













Before Ron Blomberg ruined baseball (or saved it, depending on your perspective), AL pitchers actually outclassed their NL counterparts offensively, but the DH has brought about an NL pitcher power play, resulting in a 71-point swing between the average figures for the two eras.

With each round of interleague play, observers rush to rehash the Junior Circuit’s success against its older brother. Some are quick to credit the AL’s advantage at DH for some of the disparity, but the present period of AL dominance didn’t begin in earnest until 2005, which would seem to indicate that the culprit is more likely to be a transient divergence in league strength than an ironclad institutional superiority. Here’s the average performance gap between AL and NL DHs in the interleague era:









Keep in mind that for AL DHs and NL pitchers, the numbers quoted here reflect seasonal averages, not averages during interleague play only, but that shouldn’t appreciably alter the results. The offensive performance disparity between NL and AL pitchers is essentially equivalent to that between AL DHs and the men whom NL teams choose to banish from the field for the duration of interleague play. When one makes mention of the AL’s inherent advantage at DH, one should also be obligated to observe the disadvantage that its teams face when their pitchers come to the plate (although that handicap can be mitigated to a degree by a pinch-hitter late in the game). The next time you see an AL pitcher scurry to the plate, clutching his helmet for dear life and quite possibly holding his bat upside down, remember that the man facing him down from the mound won’t be quite as fazed when their roles are reversed.

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"Most major-league hurlers were good hitters at some level of competition"

Back in my days of high school/college summer leagues, Pete Vuckovich was the poster child for the above statement, at age 18 and 19 leading our league in BA, HR & RBI, also in pitcher wins & SO. He could hit Charlie Sheen in 'Major League' but not actual major league pitchers.

Shawn Hillegas, on the other hand, hit like a pitcher when he was 19 and under, a .170 career hitter in the same summer league.