In scuba instructor training, you are taught to keep distance, just out of reach, let them tire out and then when you attempt to tackle them, you are to get behind them, yes, and the best way is often to swim under and behind them as they will try to face you while panicking. If they get ahold of you and force you down, you should swim downwards and that will make them let go of you. Advanced technique for the tackling is a bit of judo where you bait out your right arm that's pretwisted to their right arm, and as they reach for it you pull hard which makes them pirouette around and into a headlock. Now you can swim backwards towards shore with your legs while keeping their head above water with your arms, while their arms flail around harmlessly.