What a shame that the world has so many dropdead ar**holes out there.
My question how does your friend feel when he hears them, do u think he likes it!! Do u think he would rather them STOP? Have u spoken to him about it?
I assume that you and your mate league for the fun, and it sounds like those guys are spoiling it for you, and I would suspect your mate (although he may be use to it, and pays no attention, still doesn't like it, I have never met a human being who enjoys being teased!!)). Your friend has the right not be be bullied, for F**ks sake, you are bowling in an ADULT league .
So, in my roundabout way of saying it, I personally would speak to these guys regardless when u get a chance of explaining that its not too cool a thing to do in stirring a guy with a disability (if possible with humor and personality, make them aware of his knee surgeries as well). This may help the situation, and may cause it to stop, also mention it to the president of the league as well, only after you have spoken to these guys first.
If they take it badly, then they could possibly become worse towards your mate each week (assuming these guys are ar**holes)... It all comes down to whether you think this is acceptable, me I think NO, and well done for becoming involved, you sound like a good friend and decent person..
They could make it worse, they could stop stirring your mate, or they could leave the league, or you and your friend could leave the league and join another one..
But why should u leave if u love your league.. That is where the president comes into, with your treasuruer/other league officials, strengths in numbers. Approach these guys as a group let them know that their behaviour is not acceptable in ANY form of society, let alone league fun bowling, should they continue they will be asked to leave.. I'm sure they annoy/[censored] off other bowlers out there as well, and who knows whether they have caused any bowlers to actually leave the league before, because KNOWONE confronted them...Your league doesn't really need these kinds of people in there does it? These guys will probably turn more bowlers in time away from the sport
Just like the schoolyard bully, people let them get away with it by being too scared or not wanting to cause any further trouble and not reporting it...That is not a solution to a problem!!! I respect all of the posters here, but strongly disagree on this point. Hopefully I have made some sense.. Talk to your mate firstly, find out how he feels.
Now I'm all pumped up, better sit down and have some water.Hope I do not come across as some kind of extreme militant mercenary kinda guy, cause I'm not,I'm actually more of a pacifist by nature I just dislike bullies.
Good luck let us know how it all panned out