Question: Why are the gang members so spread out? I know there was the truce but surely they would he wary of anything going wrong? I know they needed to show off the different gangs but you will see one member of a gang in the middle of 4-5 members of the same gang, surely people would be more cautious than this.
Question: Why would the Riffs instantly believe that The Warriors did it? Wouldn't it have made sense, especially with the sheer numbers of The Riffs, that they search Cleon and anyone still there who they can get hold of?
Answer: The Riffs were informed of the Warriors' innocence of wrongdoing by a member of another gang who had no reason to lie on behalf of the Warriors or to frame Luther (the actual culprit). Apparently Luther had a reputation for dishonesty, among other things, whereas the Warriors were considered to be among the city's more "honorable" gangs.
Question: Instead of trying to murder them, why didn't the Lizzies simply contact the Riffs and tell them they had 3 of the warriors and to come get them? They had plenty of time.
Answer: The Riffs had put out a hit on the Warriors via the radio DJ, meaning that it didn't matter if the Warriors were taken alive or not; the Lizzies probably figured it would be easier simply to kill the Warriors and collect the reward.
Answer: There was a truce, but just in case you want different members in different parts of the crowd to see all angels and all exits in case of something. You plan if something goes wrong where everybody will be.