That's something I just do not understand at these showcases. I was well aware at one tournament that a coach was looking at me on the sideline because I recognized the coach. It could not be coincidence that this coach was within three yards of me when that my child was playing.
There is a reason some of the coaches sit on the same side as the parents. They want to know that they are getting an (almost) adult who wants to play in college and is not going to drag parent luggage with them.
Screaming about how Johnny did well on the last play is not helping - too late - either the coach saw the play and Johnny or not. Wait until you are away from the field to yell at Johnny.
Yelling at the officials beyond a mumble on a bad call (maybe!) is not what the coaches want.
After all the work at the youth level, this is the time to just watch the game and maybe enjoy it. Far better all the way around.