The contact play is a base running play in the sport of baseball. It usually refers to a runner on third base breaking for home (but occasionally refers to a runner at second base breaking for third). Similar to the safety-squeeze play, the runner at third breaks for home as soon as he sees that the batted ball is on a downward plane for a ground ball. If there is a runner at second base, he will also break for third if the batted ball is on the first base side of second. The play can backfire if the ball is hit directly at the third baseman or the pitcher as a putout will naturally be made at home plate to prevent the run from scoring. In this situation, the baserunner may freeze and return to third. At this point the runner at third's objective changes from scoring to getting in a rundown in order to provide an opportunity for the batter to end up at second base. The main advantage to breaking for home on contact is that it reduces the amount of time an infielder will have to make a play at home and, thus, increases the likelihood of the runner scoring. A secondary advantage is that the possibility of a contact play will often cause the defensive infielders to "play in," meaning closer to home plate, giving them less time to react to a hit ball and a greater likelihood of not being able to field it cleanly.
The contact play is normally used when there is one out. With no outs, it is generally considered best not to risk being thrown out at home, since there will still be two more opportunities for later batters to drive in the runner. The only exception is when there is also a runner at first, since any ball fielded quickly enough to throw out the runner trying to score is also likely to be an easy double play ball, and the team has a much higher run expectation that inning if the result of the play is an out at home and runners on first and second than if the result is two outs and a runner at third. With two outs, all runners on base automatically break on contact, since there is no point in staying at their base while the fielder gets the final out of the inning by throwing to first base.
Most students of Sabermetrics believe the contact play is proper strategy whenever there is a man on third and one out, since the loss from failure is tiny. Using standard tables of run expectation based on the number of outs and runners on base (such as Sabremetrics 101: Run Expectancy Matrix, 1999-2002), the difference between having a runner on third with two outs (the usual result of not using the contact play on a typical ground ball out) and having a runner on second with two outs (the usual result of using the contact play and having the breaking runner caught in a rundown) is only 0.043 runs. When the contact play scores a runner who otherwise would still be at third while an out is recorded at first, the net gain is 0.730. Put another way, even if the contact play failed 16 times for every one time it succeeded, it would improve a team's run scoring overall. Even that understates the advantage, since the need for the defense to play in often results in both the runner scoring and the batter reaching base safely, in which case the net benefit is 1.186 runs, which means that it could fail 27 times as often as it helped and still benefit the team overall.