How would you decide when a shuttle needs changing?
It's not something you can quantify. If the umpire feels it warrants changing, then it is changed. It's at the umpires descretion.
To be honest, if you're a professional player, the last thing you want in a match is to start an arguement with someone - least of all with the umpire! You wouldn't want to lose your focus and risk handing the match to your opponent.
@R20190, all of your points understood.
I'm referring to junior tournaments, and the umpire might not have adequate training in this area. I'd seen numerous time when the bird seemed broken from even afar, and one side requested a change, the other side thought keeping it was the best choice given they're winning at the moment. Not even a case did the umpires have the birds changed.
In the latest case, the bird had one feather broken, and the umpire couldn't tell and kept it in use!
There got to be a way to fix this... This is very frustrating to see.