On a force play when the ball initially beat the runner, but the fielder had leaped or pulled his foot off the base to field an imperfect throw, umpires can add supplemental signals to explain and sell the safe call. After initially calling the runner safe, the umpire may add the “off the bag” signal by sweeping his or her arms across the front of the body, as shown here by now-retired MLB umpire Tim Welke. The direction of the sweeping motion — left or right — should match the direction the fielder was pulled off the bag. The umpire should also verbalize, “He’s off the bag.”
Supplemental signals can help communicate your call.
In a case where the ball beat the runner but the fielder did not have secure control prior to the runner reaching the base, the umpire can signal that the fielder bobbled or juggled the ball. After signaling safe, the umpire may add a supplemental signal of moving the hands up and down, simulating a juggling action. Accompanying verbalizations can include, “No control of the ball,” or, “He bobbled the ball.”
ORIGINAL LINK: https://www.referee.com/supplemental-signals/