Bayonne president Michel Cacouault is to file a complaint after the father of Biarritz's Imanol Harinordoquy invaded the pitch to defend his son during a fight, the club announced on Wednesday.

Branding the incident "unacceptable", Bayonne said they would "file a complaint against Mr (Lucien) Harinordoquy," according to a statement on their website.

Cacouault, meanwhile, said he would seek to ascertain what Bayonne could do "legally" after the incident, which occurred in the sixth minute of his side's 21-19 defeat at Biarritz in a fiery Top 14 match on Tuesday.

Harinordoquy's father raced onto the pitch from the stands and faced up to Bayonne flank Jean-Jo Marmouyet after his son, a France international, got involved in a punch-up far from the action at the start of the Basque derby.

Harinordoquy senior's sense of family loyalty was brought to an abrupt halt by Bayonne flyhalf Benjamin Boyet, who tackled him to the ground before Biarritz hooker Benoit August stepped in to restore order.

Christian Gajan, Bayonne's director of rugby, was outraged by Harinordoquy's father's behaviour.

"I find his behaviour deplorable, that he came onto the pitch to defend his son by boxing with Marmouyet at the beginning of the match," he said.

"You could have been forgiven for thinking it was a youth match between two local villages. It was a scandalous episode," added Gajan.

Harinordoquy junior, who is known as one of the tougher customers in the sport and is a veteran of three World Cups, chose not to comment.

The president of France's National Rugby League (LNR), Pierre-Yves Revol, described the incident as "a first in professional rugby" and said that his organisation would conduct an investigation.

AFP