Whilst it does go spectacularly wrong occasionally, Metrolink generally is well used to packing and stacking high volumes of people after major events.
For example, a crush load tram is 200 pax, double set is 400 pax.
At the Etihad, the turnstiles are electronic plastic gates to get passengers through quite quick.
At Old Trafford, the turnstiles are the old 7ft high metal ones which noone can dodge through. Indeed, funny to watch a CSKA Moscow fan take a run up hoping it would spin. It was like the Road Runner cartoon where the Coyote runs head first into a brick wall... he was out cold for five minutes but too drunk to feel a thing.
At both stadiums, additional trams can be queued up by the Asda for Etihad or down at Timperley for Old Trafford. Trams can also be stacked at the war museum for Wharfside.
Generally footy fans are noisy but well behaved. Concert fans okay but less so. Cricket fans are often animals, sorry cricket fans.
Tickets are pre-printed ticket books, easy to issue at a fast speed, whilst contactless payments speeds things up nowadays.
Other locations like Bowker Vale (for Parklife) Trafford Bar & Wharfside (busy after MU matches) all have well used plans for event days.
One hidden secret is Firswood, for Old Trafford events... if theres a 1-hour queue, the short walk to Firswood gets you a mostly empty tram off the dids/airport lines.