It occurred after the Winston Cup race at Michigan International Speedway in Brooklyn. Spencer, who punched Busch in the nose, was fined $25,000, suspended from Saturday's race at Bristol, Tenn., and placed on probation until Dec. 31.
Busch has been placed on probation until Dec. 31.
"This was a very unfortunate situation," said NASCAR President Mike Helton. "Emotions are a part of every sport, NASCAR Winston Cup included. However, there is a fine line. In this instance, that fine line was crossed."
Both drivers were in violation of actions "detrimental to stock car racing for involvement in an altercation with another competitor in the garage area after the completion of the event."
Spencer and Busch have an ongoing feud dating back to a race accident at Phoenix last November.
On Sunday, Busch ran out of fuel in front of Spencer's transporter as he was trying to take his car back to the hauler. Spencer rammed Busch from behind, got out of the car, reached through the window and punched him in the face.
"We are going to appeal the penalty, and we are going to do so in accordance to the NASCAR rulebook," Spencer said. "I will always protect myself and my team."
According to Busch's car owner, Jack Roush, Busch suffered a broken nose.