You definitely can.

However, wearing any clothing associated with your team is a huge no.

Depending on your characteristics will depend on your risk of being punched or beaten up if found out. What I mean by this is a football hooligan is less likely to take umbrage if you’re a child, a pensioner, a woman or have a broken arm for example. You’re still at risk but they’d sooner punch a 25 year old guy than an elderly lady.

Finally, you don’t have to go crazy when the home team scores but you probably have to stand up and clap. Likewise you have to feign annoyance or indifference if the away team scores.