NFHS Case Play 10.4.5 Situation E page 84

[Robert E. Harrison]

A1 and B1 begin fighting and play is stopped. Substitute A6 leaves the bench area and enters the court to observe. B6 also enters the court at the same time, but B6 actually participates in the fight. Ruling: A1, B1, A6 and B6 are all disqualified. No free throws result from the double flagrant foul by A1 and B1 or from the simultaneous technical fouls by A6 and B6. Each head coach is charged with one indirect technical foul. Play resumes at the point of interuption. (4-36;10-3-9)

Why is one sub B6 allowed to fight with no penalty -- while sub A6 does not fight and gets the same punishment as if he had participated in the fight?