If you have had 3 pints, then tripped over and still think you're sober - that's a good indicator that you're pissed.
Too pissed to behave whilst watching a game of football?
I trip on curbs all the time, no matter how much pop I've had!
no, that's not what said
To put this in to context, there are some clubs where the fan base has a higher than average number of scrotes that don't need drink to be objectionable. Equally, I have personally attended a game where I'd had sooo much too much to drink, that I found an unoccupied row of seats, laid down and fell asleep missing the entire second half. Luckily the guys had to wake me up rather than go home without me, I was the only one that could drive a coach*. But other than wasting my own money, nobody suffered.
As mentioned elsewhere, it could just be that extra little tool for the stewards to be able to filter out idiots. Don't draw undue attention to yourself and you'll be fine.
*I made that very last bit up.