Chris Carpenter is proving to have thin skin, and it’s costing him.

In the third inning of yesterday’s game, Carlos Lee popped up a pitch to shortstop with runners at first and second base, and responded by slamming his bat to the ground and yelling at himself in frustration. It took less than two seconds, and his gaze was fixed nowhere near the mound. (Watch it here.)

Still, Carpenter took it personally.

The St. Louis pitcher started into a surprised Lee, who slowly approached the mound to continue the conversation. Benches and bullpens emptied, although nobody came close to throwing a punch.

Did Carpenter have reason to be annoyed? Absolutely.

Should he have reacted as he did? No way.

There’s such thing as overkill when it comes to the respect afforded by baseball’s unwritten rules, and Carpenter offered up a clear example. Immediately following the incident, the right-hander gave up a three-run homer to Hunter Pence, as part of a four-run inning. In the seven other frames that Carpenter completed, he gave up three hits and no runs.

St. Louis lost, 4-1.

Up to that point, Pence was 0-for-9 lifetime against Carpenter. To judge by the box score, the pitcher effectively psyched himself out.

(St. Louis manager Tony La Russa did have Carpenter’s back, saying, “Routinely now, hitters pop up a pitch they think they should do [something] with, and they start making noises, and that really is disrespectful to the pitcher.” With any other manager, this would clearly be an effort to deflect attention from the pitcher. La Russa, however, probably believes it.)

This is the second time this season that the Cardinals might have paid a price for Carpenter’s sensitivities.

On April 21, he was hit by a pitch from Arizona’s Edwin Jackson, and then took the unusual tack of seeking retribution from the basepaths, not the mound, going out of his way to take out second baseman Kelly Johnson on an ensuing double-play grounder. (He ultimately rattled cages but did no damage, and after the game called it “an unprofessional move.” “I shouldn’t have done it . . .” he said. “I was in a position where I didn’t control my emotions enough to not do something stupid.”)

Carpenter threw shutout ball that day, save for the two runs he gave up two innings after his basepath meltdown. It’s impossible to say that one led to the other, but the possibility exists.

Carpenter, of course, is hardly alone in demonstrating the downside to being a stickler for the unwritten rules. Take an example from 2006, in which Toronto’s Ted Lilly hit A’s DH Frank Thomas in retaliation for Oakland pitcher Joe Blanton’s plunking of Troy Glaus an inning earlier.

Lilly got Thomas with the first pitch, his intentions clear. And Thomas took it like a pro, trotting to first base without emotion, as if he’d merely drawn a walk.

Lilly, however, was thrown off his game. Six of the next eleven batters reached base, including a Jay Payton home run.

“When he hit Big Frank, he wasn’t so sure that Big Frank wasn’t coming out to get him,” said a member of the A’s. “He thinks he helped his team by hitting Big Frank, but I’ll tell you what—his heart was pumping a mile a minute until he realized that Frank was just going to take first base. And after that, Lilly couldn’t find the strike zone. He was all over the place.”

A pitcher as good as Chris Carpenter is rarely all over the place, but the emotions that accompany perceived disrespect have managed to expose a chink in his armor.

He’d be well served to cover that up.

– Jason