Balance

beat the life out of a team for 20 min...........than they get an item and win the game..........why dose this happen in this game how can you dominate the entire game then around 20 min mark all of the sudden YOU DO NO DAMAGE AND THEY DONT DIE? feels like this game is rigged to be that way because i win more games from behind than i do in the lead it seems like the first 10 min whoever is winning and ahead will lose ........why is this?