noun

(in sport) an unfair or invalid stroke or piece of play, especially one involving interference with an opponent.

the midfielder was booked for a foul on Ford

unfair,against the rules,illegal,unsporting,unsportsmanlike,below the belt,dirty,dishonourable,dishonest,underhand,unscrupulous,unjust,unprincipled,immoral,crooked,fraudulent,shady

verb

make foul or dirty; pollute.

factories which fouled the atmosphere

dirty,soil,stain,blacken,muddy,begrime,splash,spatter,smear,befoul,besmirch,blight,defile,make filthy,infect,pollute,contaminate,poison,taint,adulterate,sully,besmear