While it mostly happens in lower leagues, this used to be more common in professional sports until somewhat recently (e.g. Gianluca Vialli in association football until 1999) and may still happen temporarily.
My situation refers to the sport of quidditch (or "muggle quidditch") specifically, where captains often cover the role of coach as well, but could apply to any team sport where the player-coach would be the same time be on the field as any other player, and making strategic and tactical decisions such as substitutions, plays, strategy changes, and so on.
One key point is having one, or two, players-assistant coaches with whom to share the gameplan and guidelines to follow during the game, while the coach is on the field playing, so that at least one of these players is always or almost always off the field.
What are the countermeasures and/or aspects to keep in mind both before and during the game for a playing coach, so that their performance as a coach will not be diminished by them being focussed on their job as a player? As an extra requirement: quidditch does not currently have timeouts, so answers should not rely on using timeouts to make adjustments.