It actually took a lot for me to use that stat. I trust them on tackles but I hate the way they record missed tackles. I'll probably end up revising that...
According to nrl.com:
Player runs sideways; defender chases hard, runs him in to a dead end, dives and misses him as 2 other guys get him = 1 miss.
Ruck defence shits the bed and winger is left defending a 3 on 1. He dives at the eventual try-scorer in desperation = 1 miss.
Defender doesn't move up and throws out a lazy arm as a guy runs past him to score = 1 miss.
Yeh that's crap.