Hitting as a practice partner with a total absence of teaching or advice would be considered as facilitating play, not coaching, and will therefore not automatically invalidate your insurance. As with any insurance claim, each case is looked at thoroughly and on a case by case basis.

If a claim is brought against a coach, and that coach is found to have been providing any instruction, rather than just hitting, their insurance could be invalidated depending on the qualifications, training and experience of the coach in question.