An assist is a statistic credited to a fielder whose action contributes to a batter-runner or runner being put out, as set forth in this Rule 9.10 (Rule 10.10).
a) The official scorer shall credit an assist to each fielder who
(1) throws or deflects a batted or thrown ball in such a way that a putout results, or would have resulted except for a subsequent error by any fielder. Only one assist and no more shall be credited to each fielder who throws or deflects the ball in a run-down play that results in a putout, or would have resulted in a putout, except for a subsequent error; or
Rule 9.10(a)(1) Comment: Mere ineffective contact with the ball shall not be considered an assist. “Deflect” shall mean to slow down or change the direction of the ball and thereby effectively assist in putting out a batter or runner. If a putout results from an appeal play within the natural course of play, the official scorer shall give assists to each fielder, except the fielder making the putout, whose action led to the putout. If a putout results from an appeal play initiated by the pitcher throwing to a fielder after the previous play has ended, the official scorer shall credit the pitcher, and only the pitcher, with an assist.
(2) throws or deflects the ball during a play that results in a runner being called out for interference or for running out of line.
(b) The official scorer shall not credit an assist to
(1) the pitcher on a strikeout, unless the pitcher fields an uncaught third strike and makes a throw that results in a putout;
(2) the pitcher when, as the result of a legal pitch received by the catcher, a runner is put out, as when the catcher picks a runner off base, throws out a runner trying to steal or tags a runner trying to score; or
(3) a fielder whose wild throw permits a runner to advance, even though the runner subsequently is put out as a result of continuous play. A play that follows a misplay (whether or not the misplay is an error) is a new play, and the fielder making any misplay shall not be credited with an assist unless such fielder takes part in the new play.