Ahhh FIFA Rage. What do you know about the game? Do you take an interest?
Regarding the WiFi rage, no doubt going alongside yells of "laggggg", is, in my experience actually pre-teen convenient excuses for not being as good as they could be at the game. Better to blame lag/wifi than admit that you let in the goal and lost the game because the other person is better.
My 15yo still plays FIFA, but grts much less stressed about it. As does my 53yo husband. My 19yo doesn't bother to plsy much nowadays tho.
As with most popular multi-player games, at 11yo your son will loose a lot, because he'll be playing against others who have many, many more years of experience who will be better than he is. So he's likely to get frustrated and angry.
Of all the multiplayer games he could be playing, FIFA isn't all that bad really. At least its not COD or GTA. He's not going to get any better if he's never allowed to play, but if you talk to him about how he responds when he loses, that will help.
My husband used to sit with out boys as they played (it's how he got into it). That helps the boys understand why losing is learning and nit something you need to get angry about.
Still keep the limits, at 11 children definitely shouldn't be allowed to spend hours gaming. But what I wouldn't advocate is banning it, instead take a closer interest and teach him healthy ways to handle anger and frustration, rather than just avoiding it completely.