It seems to me in the phrase
Je n'aime pas non plus certains supporters qui peuvent être violents ou même racistes
It should be either "violentes ou racistes" ou "violents ou racists". If the reference is "supporteurs" , I would think it would be masculine, making the adjectives masculine.
Gary,
The adjective, and the noun, are both spelled 'raciste' with a terminal 'e' in French, hence the masculine and feminine are the same, in plural here with an 's'. Both adjectives ' violents ' and ' racistes ' are in masculine, plural form in this context.
https://www.wordreference.com/fren/raciste
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