Earlier this month, Jay Jaffe wrote about the Hall of Fame case for former Yankees southpaw Andy Pettitte. Pettitte, of course, was known for his cut fastball, his glare towards the hitter as he awaited the sign from Jorge Posada, and his pickoff move.

This pickoff move.

Pettitte’s pickoff move became legendary over the course of his long career, and led to teams essentially abandoning the running game against the lefty until late in his career. Pettitte retired as the active leader in pickoffs, despite baserunners often arguing that his move was really a balk. So let’s find out if Pettitte’s move was generally legal or not.

We’ll start, of course, with the rule. For our purposes, we’re concerned with Rule 6.02(a), which defines “Pitcher Illegal Action[s].”

(a) Balks.

If there is a runner, or runners, it is a balk when:

(1) The pitcher, while touching his plate, makes any motion naturally associated with his pitch and fails to make such delivery;

(2) The pitcher, while touching his plate, feints a throw to first or third base and fails to complete the throw;

(3) The pitcher, while touching his plate, fails to step directly toward a base before throwing to that base;

(4) The pitcher, while touching his plate, throws, or feints a throw to an unoccupied base, except for the purpose of making a play;

(5) The pitcher makes an illegal pitch;

(6) The pitcher delivers the ball to the batter while he is not facing the batter;

(7) The pitcher makes any motion naturally associated with his pitch while he is not touching the pitcher’s plate;

(8) The pitcher unnecessarily delays the game;

(9) The pitcher, without having the ball, stands on or astride the pitcher’s plate or while off the plate, he feints a pitch;

(10) The pitcher, after coming to a legal pitching position, removes one hand from the ball other than in an actual pitch, or in throwing to a base;

(11) The pitcher, while touching his plate, accidentally or intentionally has the ball slip or fall out of his hand or glove;

(12) The pitcher, while giving an intentional base on balls, pitches when the catcher is not in the catcher’s box;

(13) The pitcher delivers the pitch from Set Position without coming to a stop.

We generally think of a balk as an attempt to deceive a baserunner. But as you can see, while that’s certainly the purpose of the rule (MLB’s official glossary even says so), it’s also not the actual language of the rule. And really, that makes sense: if deceiving the runner were illegal across the board, all pickoffs would be illegal too. That’s because a pickoff, generally speaking, means the runner was fooled. The rule does prohibit some actions that would serve the purpose of deceiving the runner, like stepping towards a different base or pitching without facing the batter (a line Johnny Cueto and Hideki Okajima both straddled at various times during their careers). Most of the comments to the prohibited pitcher action rules mention player safety as a primary consideration, which makes sense given the pitcher is often hurling a hard sphere at 95 mph. So, it’s probably most accurate to say that the balk rule means that you can’t deceive the runner in a manner which MLB has deemed to threaten player safety, or in a way that would disrupt the balance between base runners attempt to steal and the pitcher’s attempt to get outs. In other words, you can only fool the runner so long as you don’t take one of the actions proscribed by the Rule.

All of those elements are things a pitcher can’t do without a balk being called. When assessing Pettitte’s move, we can eliminate some of them pretty quickly. Pettitte isn’t throwing home, so (5), (6), (12), and (13) are out. He has the ball, so (9) doesn’t apply. He actually throws, so (2) doesn’t apply. He’s not throwing towards an unoccupied base, so (4) is irrelevant also. Pettitte also generally keeps his foot on the pitching rubber, so (7) doesn’t apply either.

The most likely arguments for saying Pettitte balks on these throws are under (1) and (3), and fortunately, there are comments to the Rule that can help us suss this out.

Let’s start with 6.02(a)(1). Here’s the comment.

Rule 6.02(a)(1) Comment: If a left-handed or right-handed pitcher swings his free foot past the back edge of the pitcher’s rubber, he is required to pitch to the batter except to throw to second base on a pick-off play.

Does Pettitte do that? It’s actually hard to tell. Here’s one angle from a game against the Red Sox.

Pettitte comes really close there. How about here, in the 2005 World Series?

It’s safe to say that Pettitte swings his front leg towards the pitching rubber. Here, it looks like he may well have gone past at least the front of the rubber. (Interestingly, it looks like the call may have been blown twice here; in addition to failing to call a balk on Pettitte, Iguchi was safe.)

So whether Pettitte regularly swings his front foot past the back of the pitching rubber seems inconclusive. Given how close he comes, however, it’s likely he did technically violate the rule on at least some of his pickoffs.

So how about 6.02(a)(3)? Here’s what that rule means.

Rule 6.02(a)(3) Comment: Requires the pitcher, while touching his plate, to step directly toward a base before throwing to that base. If a pitcher turns or spins off of his free foot without actually stepping or if he turns his body and throws before stepping, it is a balk. A pitcher is to step directly toward a base before throwing to that base and is required to throw (except to second base)because he steps. It is a balk if, with runners on first and third, the pitcher steps toward third and does not throw, merely to bluff the runner back to third; then seeing the runner on first start for second, turn and step toward and throw to first base. It is legal for a pitcher to feint a throw to second base.

In other words, this Rule means that Pettitte, when throwing towards first base with his back foot on the rubber, had to actually step toward first base before throwing.

There, it looks like he does. But here’s that pickoff from the 2005 World Series again:

There, it doesn’t really look like he’s stepping towards first base until the very end, when he puts his foot down. And the rule doesn’t really say how “step directly” is defined. Is that determined by the pitcher’s body when his foot comes down? Or when he lifts his foot? Pettitte seems to circumvent this rule by where he plants his foot, not by where he lifts it. It’s a plausible interpretation, but it’s also equally possible that an umpire could view Pettitte as not really stepping “directly toward” first base.

A lot of Pettitte’s pickoffs came before modern camera angles, which makes a conclusive determination difficult. Still, it’s helpful is to take a look at a pitcher with a similar move to Pettitte’s: Julio Urias.

Now, interestingly, Urias also comes dangerously close to swinging his front foot past the back of the pitching rubber. But he does the same thing that Pettitte did. It’s what the announcers to those game aptly described as “a weight shift towards home but the step towards first.” Here’s a different pickoff where you can see it more clearly:

Now, there you can see that Urias steps towards first the whole time, but moves the rest of his body towards home plate. The only issue is that it looks from this angle like his front toe swings past the back of the rubber, which may well mean this should have been called a balk.

So what does this mean? Pettitte and Urias certainly, at the very least, tested the outer boundaries of the balk rule. It seems certain that at least some of Pettitte’s pickoffs should have been called balks. At the same time, the basic premise of the move – shifting your body towards home plate as you step towards first – isn’t prohibited by the rule. Jeff Sullivan has talked in these pages about pitches so good they fool the umpire as well as the hitter. The very best pickoff moves, it seems, aren’t any different.