a close call

Feindouno silencing the Celtic support as he put the ball past Fraser Forster and into the net but was judged to be offside in what appeared to be a close call for the Croatian referee.

  • They meant the referee’s decision was bordering on mistake?

Almost (that’s what it could have led to) but the meaning is that (from the commentator’s point of view) it seemed to be difficult for the referee to tell whether it was offside or not.