Most baseball fans feel they know the rules, but many of them are actually misunderstood, at least their nuances and technical definitions. Even you are fairly well-versed in the rulebook, a primer never hurts, so BP asked the MLB Umpiring Department about 10 of them. Major League Baseball umpire supervisor Charlie Reliford, a 19-year major-league umpire, and Major League Baseball umpire supervisor Larry Young, a 23-year major-league umpire, provided the definitions and clarifications.

Today, we’ll delve into the check swing and the infield fly rule.

The Check Swing

Charlie Reliford: The check swing is probably the most misunderstood rule. Many of the problems occur when language is added to the rule that is not in the rulebook. We often hear phrases such as, “the batter broke his wrist,” “the bat crossed the plate,” “the bat crossed the foul line,” “the bat crossed the batter’s front leg,” and many others. None of these are definitions or phrases from the rulebook. While any of these acts may constitute a swing on one occasion, it is possible to demonstrate any of these acts in a fashion that would not be ruled a swing. An umpire’s job is to enforce the rule as written; quite simply, did he swing? There is no definition or description of a check swing or half-swing in the rulebook. From the Official Baseball Rules:

A STRIKE is a legal pitch when so called by the umpire, which—(a) Is struck at by the batter and is missed;

There is also a prevalent belief that plate umpires should automatically defer a half-swing to the base umpire. This is not true, as covered in the rulebook:

9.04(a) The umpire-in-chief shall stand behind the catcher. (NOTE: He usually is called the plate umpire.) His duties shall be to: (2) Call and count balls and strikes; If the plate umpire (which is the umpire in chief) rules the pitch a ball and that the batter did not swing at the pitch, the manager of the defensive team or the catcher may ask the plate umpire to appeal to the base umpire. If the plate umpire rules the pitch in the strike zone or that a batter has swung at a pitch out of the strike zone then there is no right of appeal.

Runners on base are required by rule to be alert that on the call of ball, on appeal to an umpire, the decision may be reversed, changing the baserunning situation. For example, with three balls on the batter, the runner runs believing ball four has been called. If the call is reversed, then the runner would be in jeopardy to be put out.

Baserunners must be alert to the possibility that the base umpire, on appeal from the plate umpire, may reverse the call of a ball to the call of a strike, in which event the runner is in jeopardy of being out by the catcher’s throw. Also, a catcher must be alert in a base-stealing situation if a ball call is reversed to a strike by the base umpire upon appeal from the plate umpire.

The ball is in play on appeal on a half-swing. Arguing the decision of an umpire on the half-swing falls under the same rule as arguing any ball or strike call.

Rule 9.02(a) Comment: Players leaving their position in the field or on base, or managers or coaches leaving the bench or coaches box, to argue on BALLS AND STRIKES will not be permitted. To summarize: either the batter, in the umpire’s judgment, struck at the pitch for a strike, or, it is ruled a ball.

The Infield Fly Rule

Rule 2.00: An INFIELD FLY is a fair fly ball (not including a line drive nor an attempted bunt) which can be caught by an infielder with ordinary effort, when first and second, or first, second and third bases are occupied, before two are out. The pitcher, catcher and any outfielder who stations himself in the infield on the play shall be considered infielders for the purpose of this rule.

Charlie Reliford: When it seems apparent that a batted ball will be an Infield Fly, the umpire shall immediately declare “Infield Fly” for the benefit of the runners. If the ball is near the baselines, the umpire shall declare “Infield Fly, if Fair.”

The ball is alive and runners may advance at the risk of the ball being caught, or retouch and advance after the ball is touched, the same as on any fly ball. If the hit becomes a foul ball, it is treated the same as any foul. If a declared infield fly is allowed to fall untouched to the ground, and bounces foul before passing first or third base, it is a foul ball. If a declared infield fly falls untouched to the ground outside the baseline, and bounces fair before passing first or third base, it is an infield fly.

This rule’s intent is to keep the defense from letting a fair fly ball drop untouched and getting a double play. The reason for having runners on first and second or first, second, and third—but not first only—is that on a fair fly to the infield the batter should be able to beat out a double play. The runners on base may be put out for failing to tag if the ball is caught, which is why it only applies with less than two outs.

In making the determination, the fact that a ball is a fly and in the infield is only part of the umpire’s judgment. If the ball cannot reasonably be fielded by an infielder, it may be high and in the infield, yet not judged an infield fly. In making this determination, the umpire is judging whether, if the infielder lets it fall untouched, the defense will have the advantage of easily turning a double play. This decision is not limited to grass lines that commonly define the infield. These same restrictions apply to an outfielder that has positioned himself close enough to the infield to catch a ball and let it fall untouched to turn a double play.

Two other factors also limit the infield fly. First, a line drive cannot be ruled an infield fly. A line drive is a ball that is hit sharply and directly. If the fielder did not touch it in flight, then the line drive would go past him, preventing the opportunity to turn a double play. A bunt will not be ruled an infield fly. By choosing to bunt, the batter has greater control of where the ball is hit and removes the infield fly by choosing to bunt.

Fans often confuse the intentionally-dropped ball rule with infield fly. The intentionally-dropped rule has the same intent as the infield fly, but can occur with a runner on first only, line drives and a bunt. This rule prevents the fielder from touching a batted ball in flight and intentionally letting it drop to create a double-play situation. On an intentionally dropped ball, the umpire immediately calls time and declares the batter out. On an infield fly, the umpire declaring infield fly declares the batter out but the ball remains alive and runners may run at their own peril. The umpire declaring the batter out removes the force but runners may be appealed if they fail to tag and the ball is caught. If a declared infield fly strikes a runner on his base, that runner is not out; if it strikes the runner off his base, he is declared out and the infield fly put the batter out. On any other batted ball, the base does not protect the runner if struck and it has not passed the infielders. Obviously, an infield fly has to be fair as the defense cannot get a double play on a foul ball by letting it fall. 

Next up: Defining a catch and a balk.