The street gangs, and the fake tickets and ticketless, are two separate issues.
The stadium closed the gates and the kick off was delegated because fans were trying to gain to the stadium with fake tickets or without tickets. Like Liverpool fans always do (video evidence going back through big games of theirs for decades). Liverpool fans with genuine tickets were locked outside begsuse of fans with fake tickets or no tickets getting in.
The decision to close these gates and keep fans out was because they wanted to keep the fans who had already got in safe and avoid crushes. Liverpool’s bottom tier was fucking rammed, fans spilling into the aisles. It looked like one big block.
This has absolutely nowt to do with the Police’s tear gassing or the local gangs attacking fans outside the ground.