Fly at
Definition 1 of 2
Pro Tip 1/3Aggressive Action
Indicates a sudden move to attack or confront, often used for animals or in sports. 
As soon as the whistle blew, the player began to fly at the defender.
Pro Tip 2/3Metaphorical Use
Sometimes used metaphorically for non-physical attacks, like a strong argument. 
He would fly at any suggestion of wrongdoing with fierce denial.
Pro Tip 3/3Suddenness
Emphasizes the quick and unexpected nature of the action. 
Out of nowhere, the cat began to fly at the dangling string.