Some see the underarm serve as an underhanded maneuver. Others see it as lazy and a sign of weakness.
Do you teach the use of an underarm serve? How about using it to teach a student how to respond to one.
I believe it has a place in tennis, simply because it offers variation, the keystone of effective serving. Sure, if you have a monster and bulletproof serve it seems pointless to work on such a shot, but what about if you sustain an injury that limits your ability to perform or you are exhausted? Generally, it should be used sparingly or not at all if your main serve is taking care of business.
Then there is the final justification for developing such a skill, you'll become an old tennis player someday and at that stage, anything goes within the rules. Most older players rely on slice serves almost exclusively as their strength dissipates
Murray used an underarm serve as his first shot at Wimbledon this year thanks to a stomach muscle injury. Here is Bublik using six of them in one game against Tiafoe at Wimbledon 2022. I presume he resorted to this because his opponent was easily handling his regular serve.
