Rito I need help with ur app

So I was playin league, with 150 fps. BUT THEN IT DROPPED TO 01 FPS AND IT LAGGED OUT. i tried to get back in but couldnt for 30min. (leaverbuster?) So i uninstalled the game then downloaded it again and this is wut it says (quote by quote from IMAC)

"League of Legends" is damaged and can't be opened. Chrome downloaded this file today at 6:40 PM from signup.na.leagueoflegends.com

PLZ if you know a way to fix it plz tell me, I want to play league for the Vs. event*[zombie-nunu-tears]*