The Amazing Spider-Man #216 (1981)
Writer: Denny O’Neil
Artist: John Romita Jr.
Peter learns of an assassination plot that’ll happen during a race. He doesn’t know who the shooter is, or who will be shot, or where the shooter will be. So he goes to the New York City marathon to at least try. He helps out a lot of random people as he follows the 16,000 runners. Then gets a call from Madame Web telling him what he needs to know. He defeats the shooters on a water tower.