Marty's father George he was killed in march 15 1973 biff took the time machine to give his younger it self biff he went back to his past in november 12, 1955.

biff wants to kill marty but marty he travels back to november 12, 1955 and biff was watching to receive the almanac from it's self in 2015 and 

marty follows biff's car he finally gets the almanac away from biff when he drives through the tunnel and leaving biff to crash into a manure truck.

during the tunnel chase and biff tries to run and marty down his foot is shown not in the strap on the hoverboard when marty is rescued by doc his 

foot would not have to be in the strap in order not to leave it behind.