I found half. 7.04 B USSSA 7.04.B At any time, the offensive team may use a courtesy runner for the pitcher and catcher of record the previous inning on defense. The courtesy runner must be a player not presently in the line-up. If no players not presently in the line-up are available, the courtesy runner shall be the player making the last batted out. The re-entry status of the courtesy runner, pitcher, and catcher shall not be affected by this rule. If at any time, a courtesy runner is determined to be ineligible, a proper replacement pursuant to these rules (if available) shall be used without penalty.