a) not a felony. you cant chase somebody down to arrest them unless its a felony (read the law above). you can still arrest somebody for a misdemeanor (most commonly a store-owner can detain a shoplifter) but the law specifies that somebody escaping cannot be arrested unless it was a felony (they want to avoid exactly the situation that happened, putting people needlessly in harms way)
b) they didnt witness the trespass in question. they just saw him running on the street. has to be committed within their presence or immediate knowledge (read the law above)
c) you cannot use more force than is reasonable to make the arrest
citizen's arrest at gunpoint over trespassing?