What's your call - player entering without being beckoned?

[dkmz17]

Saw this Saturday at a HS Varsity playoff game. Team A has the inbound on Team B's baseline. Referee is preparing to hand ball to A1 for the inbound. As Referee is handing ball to A1, Coach B decides to substitute and sends B6 up the sideline (Team B bench is on sideline on opposite end from throwin) to report. A1 inbounds the ball and the ball is in play when B6 just runs onto the court without being beckoned and with no horn from the table. B6 never really maade it to the table, but enters the court before midcourt. What is the proper call under NFHS rules?