Force Out
A runner who has to move loses his right to the base, and the fielder only has to touch the bag.
What it actually is. A runner is forced when the batter becoming a runner takes away his base, so he has no choice but to advance. On a force, the fielder does not have to tag him: touching the base ahead of him with the ball is enough. A man on first is always forced. A man on second is forced only if first is also occupied.
What somebody who knows the game gets out of it. The force is the reason a double play exists and the reason the bases loaded situation is dangerous for the defense as well as the offense. It also drives infield positioning: with a man on first the second baseman and shortstop play at double play depth because the force at second is available, and with a man on third and the infield in they are giving up the force at second in exchange for a play at the plate. Almost every infield alignment decision is a decision about which forces to protect.
The numbers worth knowing. There are only four force situations and they follow from who is on: batter to first always, man on first forced to second, first and second forced to third, bases loaded forced home.
What people get wrong about it. The force is removed the instant the lead runner is put out. If the fielder touches third to force a man from second and then throws to second, the runner who was on first is no longer forced and has to be tagged. Getting this wrong is one of the most common ways a defense loses an out it already had, at every level including the majors.
At Little League and travel ball. This is one of the two or three most valuable things to teach a young infield, because the reflex to tag a forced runner costs a step every time and the reflex to touch the bag on a non force play costs the out entirely. Read the Play on this site drills exactly these situations with the runners shown.
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