Offensive Interference

The batter hits the ball, and starts sprinting towards first. The ball doesn’t get very far, and a fielder— usually the catcher, but occasionally the pitcher— grabs the ball and fires down to first. But! The ball hits the runner in the back, and as they run through first base, everyone is pointing and shouting, while the other runners scramble to take advantage of the situation, and the defense tries to regain control of the ball as quickly as they can. The runner looks like they will be safe at first— but the umpires are making the “out” signal. What’s going on?

What’s happened is that the runner has fallen victim to one of the oddities of baseball’s geometry, and as a result, has been called out for interference. To explain: the path that a batter/runner nominally has to follow when they are running to first is in foul territory, but the base itself is in fair territory, and most batters— especially right-handed batters— will need to cross through a little bit of fair territory in order to get to the base path to begin with. On a play where speed is of the essence, wouldn’t it be better not to have to make the little circuitous route out of your way, just to get to the “proper” running path? Well, indeed, sometimes a batter/runner will start sprinting down to first on the fair side of the foul line. This is not where they’re supposed to be¹, and can put them directly in line with the throw to first, if the ball gets hit into the wrong place. Technically, the throw doesn’t have to hit the runner in order for an interference call to be made; if the umpire judges that the runner’s placement interfered with the fielder’s ability to either throw to first, or to catch the throw at first, then they can call the runner out.

Another flavor of offensive interference that happens frequently enough on bunts that it's worth mentioning: the batter bunts, and as they are running out of the batter's box towards first, they come into contact with the bunted ball. If this contact happens behind the plate, it's a foul ball, but if it happens down the line, the batter is out, as the batter is now a runner, and if a runner touches a batted ball before it is touched by a fielder, then that runner is out for offensive interference.

On a call of offensive interference, the ball instantly becomes dead, and the runners have to go back to whatever base they started from.