The rivalry between Southampton and Portsmouth football fans has entered a "new era", Hampshire's police and crime commissioner (PCC) has said.
The two south coast rival teams meet for their first league match in 13 years on Sunday, with a history of violent clashes between fans at previous games.
PCC Donna Jones said there had been "tremendous" planning for policing the event which began when it was known both teams would be playing in the Championship this season.
She said the rivalry between the fans should be "healthy and safe" but anyone coming with intention of causing trouble should expect to be arrested and its consequences.