https://www.youtube.com/watch?v=Xe3jTzYZ9w8
It's getting a WR crossing close to the line of scrimmage, whilst obstructing defenders - illegal pick taking two defenders out of the game leaving a receiver uncovered. Been a staple of Pats plays for years, very rarely called.
EDIT: In that clip, you see no 80 coming across, taking with him the defender covering him in man to man. He then throws his hands up, is clearly not running a route whatsoever - meaning the other defender is obstructed leaving a receiver all alone.