Earlier quoted context omitted.
I have always wondered why we have not had a repeat of the underarm delivery [1], but just done by bowling overarm very, very slowly. As far as I know there is no rule in how fast the ball has to be bowled and if you bowled very slowly the ball would reach the batsman rolling along the ground. 1. For those that don't know the history of the underarm delivery, in a match between Australia and New Zealand the final bal…
A very slow ball with no spin is very easy to hit for six, especially if you're delivering the ball with an unnatural movement so the batsman knows your intention from your arm movement. Fast bowlers bowling towards the end of limited overs cricket and facing aggressive attacking shots actually do bowl occasional "slower balls" using their normal delivery stride to try to catch out opponents who tend to mistime shots…
County champ tennis player and LTA coach here. You might not see this much from tour players (though Razzano had a crack at it in Paris this year [0]) but I can assure you a well executed 'drop shot' serve will befuddle even the most experienced player. So much so that it is considered unsporting [1]. In fact, 'under hand' serving is allowed in tennis but it is conventional - though not a rule - to inform your opponent that you are doing so for this very reason.
For a quick take on why, your expectation (long serve) will be violated. While you're getting over that you'll need to be running up court (getting on for 12m depending on where you were standing to receive) starting from a stance that was balanced to go left or right. By the time you get there, you're likely going to be hitting the ball on the drop with an over extended racquet which limits your shot selection quite drastically, and the whole back of the court is now open, rendering you vulnerable to a lob or passing shot - the very things that make drop shots such an effective weapon.
I know a few players who are constantly working on their drop serves, but it is a super hard shot to play well, which is at least one of the reasons you won't see it much at pro tournaments, another being that spectators will literally boo you.
(edit: balance parens)
[0] http://m.tennis.com/photos-video/2015/05/videos-razzano-late... [1] http://m.tennis.com/pro-game/2014/07/gentlemans-disagreement...