Serena Williams lost a tennis match yesterday at the 2018 US Open, but not without some controversy.
[Williams was] penalized in the second set because of three separate game violations.
Source
The first violation is mostly where I'm confused.
Williams got the first violation from umpire Carlos Ramos, who ruled that Williams received coaching earlier in the set; she told him she'd "rather lose" than cheat.
What does that mean? Coaches can't "coach" during a match? Does that mean no communication is allowed between coach and player? Why have a coach then if they can't give you a second perspective during a match? Seems like such a strange rule.
How closely is this rule followed? Williams' coach seems to think it's both a bad rule and generally not enforced. Is this true? Are there other sports leagues with a similar rule? I'm coming from an American football and baseball understanding, where coaching is vital to play.