Why were roosters fans clapping BJ for being sin binned?

[TheLoneRooster]

A flop-tackle after a break is an automatic sin-bin. The players all know this although it seems many fans still don't know.

Dumb play which nearly cost us the game.

You're absolutely right about it being an automatic sin-bin and BJ's was a sin-bin offence. The thing is it isn't always adjudicated that way by all refs on all occasions. As usual, consistency of the application of the rules is what I'm looking for here.

[Headless Chook]

would be a terrible rule

Please explain?