If somebody is clearly chucking then the approach I take is to talk to the oppo skipper at the end of the over and inform him of the fact. The key word there is FACT, many bowlers have a strong wrist action that flicks the ball out and you need to be certain the arm is being used in a bending/throwing motion. If you are then in most cases a quick word with the skipper and the bowler either straightens up or gets yanked. The important thing is to do it with as little fuss as possible imho. I don't agree with outright no-balling without speaking to the captain first. It causes bad feeling and mis-understandings. The bowler may have not had any problems before and will be in a state of shock. I saw a youngster 2 seasons ago chuck a quicker ball and I spoke to the skipper and he had a word with the bowler, who bowled fine afterwards. It was only later in the season I discovered he had been chucking against most of the teams and we were one of the few to mention it!. Had blatant chuckers before and I've asked the skipper to withdraw them at the end of the over. 99% of the time this has worked fine.
We had one of our lads called Saturday. I thought it was harsh as his action is pretty orthodox, the call was on the margins and the guy bowls military medium. I've faced him in the nets and he looks perfectly normal, even side on he's looked fine until what went down Saturday. What was odd is that the umpire called it from behind the stumps, it didn't come from square leg. I was standing at square leg and some that looked fine got called and others that were more suspect didn't. The ump could've handled it better imho as he could've defused things by speaking to our skipper and the oppo skipper first (who was batting). The poor lad was shattered, his one over went for 16 and could've been handled better. We'll be working hard with him to sort it but I think he'll be fine.