Bangor City's 4-2 Welsh Cup win was marred by a pitch invasion where Llanelli players were targeted by opposing fans.
Christian Sergeant's equaliser in the last minute of normal time sparked City fans to spill onto the pitch.
In the melee that followed, Llanelli goalkeeper Duncan Roberts appeared to be pushed over and Andy Legg was allegedly spat at in the face.
Dyfed Powys Police have confirmed they are to launch an investigation following the ugly scenes at Newtown's Latham Park ground on Sunday.
The Football Association of Wales will watch video footage of the incident and await reports from the police and match referee Phil Southall before deciding if they will take action.
Llanelli defender Legg, the former Wales international, said: "I'm disappointed in the fans.
"I understand the fans are jubilant as they've scored a last minute equaliser but to come on and poke and spit in my face is a bit out of order.
"The fans have let Welsh football down.
"I'm delighted for Bangor who have now qualified for the UEFA Cup but if the fans behave like that in Europe what will that do for Welsh football?"
The match was already a heated affair when Bangor's Peter Hoy was sent off after four minutes for a rash challenge.
Ashley Stott them put them ahead, before Dave Swanwick's own goal brought Llanelli level.
Rhys Griffiths put Llanelli on course for the treble but they had Wyn Thomas sent off for using foul language.
Sergant levelled for Bangor in the last minute sparking the pitch invasion and the police became involved.
The drama continued in extra time when Marc Limbert scored from the spot and Karl Noone secured a 4-2 win for the North Walians.
Llanelli were reduced to nine men with five minutes to go when Griffiths was sent off for an elbow.
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