Alleycats are illegal races, cept that if it came own to brass tacks it's a ride not a race. You navigate your own course in open traffic and are required (as far as the law is concerned) to observe all yadda yadda as whenever you ride. So if you get into an accident doing something you weren't supposed to it's your own ass in a sling anyway. Police could stop a race(ride) from starting for lack of parade permits or sumsuch if they wanted, but only at the start as it's the only time the racers are packed together, many races start one rider per minute, or with each rider having a completely different manifest, etc to avoid mass starts.
The general rule is if you do something that gets you hurt, you get sympathy. If your involved in a not at fault accident or an at fault during one, you don't know what the hell they're talking about "Alleycat? there were no cats in the road, is he saying he hit me trying to dodge a cat? Check him for crack!"