He does NOT have to make an obvious action. The subsequent bullet (thanks for the drafting IFAB!
) makes crystal clear that
being in the way is enough for an OSP player to interfere with an opponent.
@bester pointed this out above:
a player moving from, or standing in, an offside position is in the way of an opponent and interferes with the movement of the opponent towards the ball this is an offside offence if it impacts on the ability of the opponent to play or challenge for the ball; if the player moves into the way of an opponent and impedes the opponent’s progress (e.g. blocks the opponent), the offence should be penalised under Law 12
The "clearly impacting" doesn't apply, merely "impacts" as per language above. IFAB clearly doesn't want OSP attackers getting in the way of defenders. (But they have done a poor job of drafting, as 99% of referees will say there are only 4 ways to interfere with an opponent from the main four bullets, but there is this fifth way set out separately.