offside

from WordNet (r) 3.0 (2006)

offside
    adv 1: illegally in advance of the ball or puck
    adj 1: illegally beyond a prescribed line or area or ahead of
           the ball or puck; "the touchdown was nullified because
           the left tackle was offside" [syn: {offside}, {offsides}]
           [ant: {onside}]
    n 1: (sport) the mistake of occupying an illegal position on the
         playing field (in football, soccer, ice hockey, field
         hockey, etc.)

from The Collaborative International Dictionary of English v.0.48

offside \offside\ offsides \offsides\adj. (Sports)
   Illegally beyond a prescribed line or area or ahead of the
   ball or puck; -- in sports such as football or hockey; as,
   the touchdown was nullified because the left tackle was
   offside.
   [WordNet 1.5]