A team masseur prevented a certain goal by kicking the ball off the line during a Brazilian fourth division match and was then chased off the field by the enraged attacking team.
Tupi said they would take legal measures following the last-minute incident in the tie against Aparecidense which led to them being eliminated from the competition.
"It was our only chance. If I hadn't done it, Aparecidense would have been knocked out," the masseur, Romildo Fonseca da Silva, was quoted as saying by Brazilian media.
"I don't regret it because I did it out of love for the club."
Tupi described the incident as "one of the most shameful episodes in the history of Brazilian football" on their website and said they would lodge a protest.
Television pictures showed the masseur, wearing the Aparecidense uniform, standing next to the goal when Tupi launched an attack late in the game.
As Tupi threatened, he moved into the goal, cleared one shot off the line and then stopped the rebound with both feet before scrambling the ball away, for a double save any goalkeeper would have been proud of.
He then turned, ran behind the goal, hurdled the advertising hoardings and sprinted to the dressing room entrance, chased by furious Tupi players. Riot police prevented the livid players from following him down the tunnel.
Play was re-started after a 20-minute delay but Tupi were unable to create further chances.
The game ended 2-2 and Aparecidense went through on away goals after a 3-3 aggregate draw in the round of 16 tie.
The Brazilian fourth division consists of a group stage following by a knockout competition.