[GAMEPLAY] Hack or bug? Unable to move/cast skills.

In my recent ARAM game, three people in my team, including myself, got this problem: Suddenly we couldn't move, cast or do anything with our champs.

It wasn't a status effect, since no enemy was close enough, although they naturally caught up to us fast and killed us in these situations. Wasn't lag either, since everything else moved smoothly and I at least was able to talk in chat to warn that I was "rooted". Also, it was pretty obvious that the problem was in the game, when at one point, me and my last living team mate were about to run back to our turret and both froze mid-way at the same time. This happened to me about ~5 times during the game.

This seemed to happen in run-or-die-or-kill situations, which made some of us suspect a hack. However, at the end screen, the enemy team's LeBlanc said she had had similar problems during the game as well.