This is definitely a tough one to judge. Last season, in one of my games (if I recall correctly), a ball was headed across the box by an attacker; a defender standing pretty much on the penalty spot attempted a clearance and completely fluffed it, simply flicking the ball into the path of an attacker behind him, who converted easily. Defender's CAR raised flag; my first thought was goal because of the deliberate attempt to play the ball, and I saw nothing to suggest that the scorer had, in law, interfered with the opponent. Neither was it a 'save'. Yes, the striker was close to the defender (placing a psychological burden that may have contributed to the poor clearance), but he hadn't challenged for the ball (that itself can be hard to discern, as a player is rarely doing nothing), wasn't touching the defender, and hadn't touched the ball until the defender's miskick. Obviously I went over to have a word and asked the CAR which player he had flagged; he said that a couple of players had been offside, including the one who scored. I told him I would accept his decision, since I couldn't be sure whether the attacker who had headed the ball initially wasn't offside, but explained that for me the second attacker hadn't been offside due to the defender's kick. On balance, I probably would have been well within my rights to overrule the CAR that day, but hopefully the CAR learnt something for his next outing.
I understand the theory quite well, but in my opinion the interpretation of 'interfering with an opponent' remains fraught with difficulty in practice, as a player's intentions/movements aren't always clear.
