When did this pushing-pulling racing style start in Nascar?

Answer 1

2011 is the first year Daytona has seen what is a new style of lock-bumper superdraft racing. The lock-bumper superdraft, where two cars are literally locked together all the way around the track, debuted at Talladega in April 2009 but in previous races the two-car superdraft would take the lead, then the second car would pass the leader upon the tandem clearing traffic. What happened at Daytona is in the superdraft the pushing car refused to pass the leader, instead staying on his bumper running interference for the leader, who was usually a teammate of the pushing car. When four or more such tandems were created, they created an aeropush effect on cars behind them - air is now reassembling behind each tandem as a wall instead of the normal drafting vacuum; the result was that cars outside the top ten were being stopped from catching up to the leading groups.

NASCAR attempted to break the 2-car superdrafts by narrowing the front grilles of cars to make them overheat without pulling out to pass; it didn't work as trailing cars instead simply moved briefly to one side to take in fresh air, plus drivers began radioing each other to coordinate prearranged "swaps" instead of fighting each other for position.