Although the underarm service can be a great weapon, it is not used by many players but becomes more frequent on tennis courts every day.
Nick Kyrgios and Alexander Bublik are probably the two players that use this tactic the most. Both use it quite often and can produce some easy points, or even aces when using the underarm serve. However, many more players started to use this also during the 2020 season.
For example,
Alejandro Davidovich Fokina is one of the players that used this tactic, but also
Daniil Medvedev adapted the underarm serve to his repertoire. The Russian was also the first player ever to use it during the ATP Finals in his match against Alexander Zverev.