[BillyMac]

NFHS 9-5 5: Illegal Dribble: A player shall not dribble a second time after his/her first dribble has ended, unless it is after he/she has lost control because of:
ART.3...A pass or fumble which has then touched, or been touched by, another player.
NFHS 4-21: A fumble is the accidental loss of player control when the ball unintentionally drops or slips from a player’s grasp.

I'm sure that A1 did not intentionally dribble the ball off his leg, so it must have been unintentional and accidental. There is no player control during an interrupted dribble (4-15-5: An interrupted dribble occurs when the ball is loose after deflecting off the dribbler or after it momentarily gets away from the dribbler. There is no player control during an interrupted dribble), so A1 did lose player control. As Camron Rust has pointed out: "A fumble is something that occurs when someone is holding the ball". So the key word here is grasp. The ball may have slipped from his hand, but not from his grasp, during his dribble, causing the situation you have presented.

Everything hinges on the word grasp. It appears that Camron Rust is correct, "you have found a hole in the rules". If this had happened in my game, I would allow A1 to play on, and with the exception your IHSAA clinician, I'm going to guess that most officials would do the same as me.