unsportsmanlike

from WordNet (r) 3.0 (2006)

unsportsmanlike
    adj 1: violating accepted standards or rules; "a dirty fighter";
           "used foul means to gain power"; "a nasty unsporting
           serve"; "fined for unsportsmanlike behavior" [syn:
           {cheating(a)}, {dirty}, {foul}, {unsporting},
           {unsportsmanlike}]