Someone asked the following about what a coach should do during matches.
What’s your ideal balance as a coach between motivating players vs. giving correctional feedback in timeouts, between sets, or in preparation for a match? Motivating players would include giving motivational speeches, empowering players to believe in themselves, etc. Providing players with correctional feedback would be just that.
Generally speaking, you want to steer clear of individual skill related feedback during matches. That’s for practice. You don’t want the player thinking about what they’re doing. This said, if you can provide a quick cue to remind them of something, no problem. It has to be something they know well, though, and can instantly take on board without much conscious thought.
The more game-play oriented feedback is a different story. That’s stuff like positioning, decision-making, tactics, etc. These are areas were a little more thinking isn’t so detrimental. Still, make it quick and to the point.
As for the more motivational side of things, I believe it was Joel Dearing who said in his Volleyball Coaching Wizards interview that the coach’s top job during matches is the emotional management of the team. That works in both directions. Sometimes you need to pump them up, boost their confidence, etc. Sometimes you might need to rein them in a bit. Other times you need to get them to take a few deep breaths and relax.
The skill is knowing what you need to do in the situation you’re facing.