Baseball is a game of countless axioms. You can never have enough pitching, you shouldn't make the first or third out at third base, and good things will happen if you throw strikes. Much of this wisdom has been challenged over the years, some of it verified. One self-evident truth is tested more in September, with its expanded rosters and flabby lineup cards, than in any other month: pinch-hitting and starting aren't the same. Considering their rarity—particularly in the American League—it's impressive that any truism about pinch-hitters could tally considerable mileage, yet one does. To wit:
"[Hitting coach Pedro Grifol] has been doing a good job of preparing these young guys about pinch-hitting. First fastball in the strike zone, you better be ready to hit, and David was last night. First-pitch fastball—boom, base hit. That's what a good pinch-hitter does." – Ned Yost
Rookies, veterans with more than 200 pinch-hit at-bats to their account, managers, and players from past eras sing in agreement: Pinch-hitters must take advantage of the first fastball. The thought process makes sense—after all, the oversimplified key to a good approach is getting a hittable fastball—and sounds good when other factors are considered. However, the axiom itself is not grounded in reality, at least not these days: according to Andrew Koo's research, pinch-hitters have swung at one more first fastball per 100 pitches than starters over the past three seasons. But while the pinch-hitter choir gets the words wrong, their message—pinch-hitters stray from the norm—is correct.
Most of the statistical differences between starters and pinch-hitters border on imperceptible. For instance, pinch-hitters swing at 46 percent of the pitches they see—the same as starters—while swinging at 64 percent of the pitches they see in the zone—an additional swing per 100 pitches compared to starters. The gap between the sides only becomes noticeable when putting the bat on the ball is examined. That's because pinch-hitters' contact rates are five percentage points worse than when those same hitters are starting.
Why is the difference between contact rates greater than everything else? If pinch-hitters were more likely to swing, or leastways more likely to expand the zone, then the contact rate slippage would be self-explanatory. On a macro basis, though, hitters seem to maintain the same tendencies. So what gives? There seem to be three contributing factors:
1) The pitchers. Duh. Most pinch-hitters tend to face a certain kind of pitcher—i.e., relievers—which means less contact is expected before they step to the plate. Or, as Chad Tracy tells it: “These guys are one-inning guys. Their breaking balls are sharper. Their heaters are harder. They’re coming in trying to strike you out or embarrass you." There's also the platoon advantage, especially in the NL, where pinch-hit decisions are telegraphed by the pitcher's slot coming up in a late-and-close situation.
2) The situation. Although the overall tendencies might remain the same, it's possible the hitter's pitch selection changes in ways unaccounted for. Hypothetically speaking, a batter might be more willing to swing at a first-pitch curve, or a fastball down-and-away if a hit is deemed even more valuable than a walk than usual. Likewise, batters would be more likely to swing from their heels—thus increasing the likelihood of a whiff—if a home run could tie or win the game. This explanation loops back to what Russell Carleton wrote about last month, on how clutch hitting might exist, albeit in a different manifestation.
3) The other aspects of the pinch-hitter penalty. Facing live pitching after a few hours spent on the bench isn't easy. It seems reasonable to think a hitter's focus (and bat control) might not be as sharp as usual. Besides, many pinch-hitters are worse hitters than your starters anyway.
Weigh those factors to your own liking, but altogether they would seem to offer a decent explanation for why, with almost all else equal, pinch-hitters tend to swing and miss more than starters. Hence why batters have been found to lose 34 points of wOBA when used as a pinch-hitter, according to The Book.
So the next time you're watching a game and a pinch-hitter is summoned, don't expect to see him act much different than he would otherwise. Instead, prepare for a little less contact and much more of the same.
Special thanks to Andrew Koo for research assistance