In general, it seems that umpires are more brave with calling faults in tournaments that TTR is available. It's good to see umpires being more strict in my opinion.
However, majority of the time, when umpires jump in, it's usually regarding the toss angle. Compared to hidden serve, it is a seemingly unimportant rule though in my opinion.
Of course, players shouldn't be able to jolt the ball sideways into their racket, to generate crazy spin, but even with a toss, e.g. 45°, it creates very little advantage, compared to a completely vertical toss.
In todays match between Harimoto and Duda, the umpire jumped in early to fault Harimoto on toss angle. After challenging succesfully (23°), I was stunned to see the umpire jump in, when not even close to being correct, about the toss angle!?
Truls - a player with probably one of the most legal serves (hiding wise) was also faulted during his match against LJK. Yes, he lost to challenges earliar, also to toss angle, and was faulted in the 5th game with no challenge to overturn the call.
The umpires positioning is terrible, for determining whether a serve is hidden or not though, so I'm not sure what the fix is. Players being able themselves to challenge hidden serves is good in my opinion.
Unless the toss is blatantly sideways, I disagree with umpires being completely fixated with the toss angle. They should focus on serves being hidden more.
Hope everybody enjoys the rest of the WTTTC, it's been good so far. :)