Baseball metaphor, equivalent to 'lay your body on the line'

The English expression 'you need to be prepared to lay your body on the line' is a football metaphor, referring to the potentially painful act of lying down on the goal line to prevent a goal being scored against you.

I have heard there is an American expression which means almost the same thing involving baseball. Can anyone please remind me?

Maybe you are thinking of "taking one for the team"?

That's not baseball specific though, except that it can mean allowing yourself to be hit by the ball while you are at bat, so that you are automatically advanced to first base (and therefore advance the runners, potentially scoring).

If you're thinking specifically about blocking a score, "covering your bases" is from baseball and means to literally cover the base to attempt to prevent a runner from scoring (or advancing). It doesn't have a particularly painful connotation though, whereas taking one for the team certainly does.

Mention of 'plate' has reminded me. Don't you talk about 'stepping up to the plate'? 'Taking one for the team' sounds a good one too. That means more or less the same thing as being 'prepared to lay your body on the line'. Sporting metaphors are very effective. Cricket has a vast number.