Giving more than a little hint
One of the core jobs of a coach is to help his/her players improve their performance. Sometimes, though, that desire can make things worse instead of better.
Take the third base coach who knows that 1) the pitcher has a tendency to throw high pitches and 2) the hitter has a tendency to go after high pitches she can’t hit. In his desire to help, the coach will shout out “Lay off the high ones!” Well, if anyone is paying any attention at all it shouldn’t be too hard to figure out what the next pitch will be.
On the other side, a coach who yells to the catcher to keep the ball down and out on the next hitter is also asking for trouble. A big part of pitching is keeping the hitter off balance and guessing. If she knows where the next pitch is going (assuming the pitcher can hit that spot!) it should be a whole lot easier to hit, because the zone she has to cover has narrowed considerably.
Those are just two examples. A coach who tells a hitter to make sure she moves up in the box in an obvious bunt situation, or tells the baserunner to make sure she gets a good jump on the next pitch is taking the element of surprise out. Again, assuming the opponent is paying attention, the coach might as well just say flat out “Hey, we’re bunting” or “Hey we’re stealing.”
It can be hard to hold your tongue sometimes, especially when the outcome is really important. But you have to learn to do it. Otherwise, you’re doing more to help the other team than your own.