RugbyRebels

Am watching NFL and wondering if challenge flags are the answer to rugby's TMO challenges. Give coaches two challenges a game. They can throw the flag at any time but play is only reviewed at the next stoppage. Get it wrong and play goes on. Get it right and you get your challenge back (up to say 4 a game).

Would empower the refs again and give an added element of intrigue, with the onus on coaches to challenge. Egregious missed foul play would still be called up, because you don't lose a challenge for throwing the flag. Fans wouldn't be able to complain as much about Tmo's - their coaches should have challenged better. It would prevent the issue in the RWC final for the ruled out NZ try - play would have gone on and the try been awarded unless the SA coaches challenge it, in which case good play by them.

What's the flaw that I'm missing?

They tried something similar (captain's challenge) a few season's ago in some competitions (super rugby and rainbow cup were two, I think) and it got scrapped after the trial. It did really seem to slow things up a lot and teams started using it to slow the game right down when they were under pressure. That was used in addition to TMO though and I vaguely remember there being something weird like what you could challenge differed at different stages of the game (foul play and things in the act of scoring and anything in the last ten minutes or something). So, similar, but also a bit different, to what you're suggesting.