My friend keeps having a problem when he plays league

So recently i asked a friend to play league but the uninstalled because they had a reoccurring problem when he didn't do anything for say 20 or 30 seconds it went to his homepage and you would have to click back on the game and get back in. Now this isn't like reconnecting it just takes a couple seconds to get back in but it keeps happening over and over again and is quiet nuisance. If any one has an idea what causing this or, even better, a way to fix it please tell me.