I've coached youth sports for all of my kids, but mostly while they were under 11 years old. I believe the only time I raised my voice while coaching was to tell my son, "Please do not talk to the ref. Please do not talk to the ref."
I had a couple of experiences.
This is fairly minor in comparison to other stories. In 5th grade rec soccer, we had a fairly competitive team. No "star" players and each kid knew how to play and play in position. About 6 games in, we were playing another undefeated team and their "star" player was rendered ineffective. His hero ball was easily countered with a double-team. Kid was getting really frustrated and ultimately received a yellow card for conduct and the coach pulled him. After the game, kid's older brother grabs a soccer ball and throws it into the back of the HS age official. The kid's parents did nothing, so I recommended the ref stand near me while I called the commissioner.
My oldest also played 6th grade Pop Warner tackle football, in the (misplaced) theory that it would prepare him for MS football. One of our games was against a team from Pflugerville. They showed up with a non-dad head coach - young, former athlete - in tow. I am not sure that any of the coaches had kids on the team; that was a yellow flag for me. En route to a 48-6 loss, about 6 of our players were injured, including 2 concussions. Some from poor form; some from just getting beat up. Two things stand out from that. First, the Pflugerville fans treated every TD or big play like it was the first time they'd ever seen a TD: screaming, high 5s, dancing, etc. Second, once you are winning by a large amount, the clock is free running and all plays must be run between the tackles. Opposing coach spread the OL so that the tackles we on the hashes. Nice.