
1) Ace feature 2) Arc producer 3) Ball bearing 4) Cause of a curved flight path 5) Court technique 6) English at Wimbledon 7) English creator 8) English on a tennis ball 9) Feature of some returns 10) It may be put on a return 11) Lob motion 12) Result of an upward stroke 13) Rotation on a fastball
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https://www.crosswordclues.com/clue/topspin

Spin of a ball where the top of the ball rotates toward the direction of travel; the spin goes forward over the top of the ball, causing the ball to dip and bounce at a higher angle to the court.
Found on
http://en.wikipedia.org/wiki/Glossary_of_tennis_terms

In ball sports, topspin is a property of a ball that rotates forwards as it is moving. Topspin on a ball propelled through the air imparts a downward force that causes the ball to drop, due to its interaction with the air (see Magnus effect). Topspin is the opposite of backspin. ==Baseball== In baseball, the curveball, a type of pitch which usuall...
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http://en.wikipedia.org/wiki/Topspin
[Transformers] Topspin is the name of several fictional characters from the Transformers universes. Due to legal issues, later incarnations of the character are called Autobot Topspin. ==Transformers: Generation 1== The portraits of Topspin and Twin Twist on their techspecs were originally reversed, causing some children a bit of confusion....
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http://en.wikipedia.org/wiki/Topspin_(Transformers)

when the tennis ball spins forward. This can cause it to bounce higher as well as dip down quickly.
Found on
http://www.ducksters.com/sports/tennisglossary.php

The forward rotation of the ball in motion.
Found on
http://www.encyclo.co.uk/local/21422

spin of a ball where the top of the ball rotates toward the direction of travel; the spin goes forward over the top of the ball, causing the ball to dip and bounce at a higher angle to the court.
Found on
http://www.translationdirectory.com/glossaries/glossary148.htm

[
n] - forward spin (usually of a moving ball) that is imparted by an upward stroke
Found on
http://www.webdictionary.co.uk/definition.php?query=topspin
noun forward spin (usually of a moving ball) that is imparted by an upward stroke
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https://www.encyclo.co.uk/local/20974

To hit the top of the ball making it spin forwards while moving forwards, and forcing the ball to curve down over the net.
Found on
https://www.encyclo.co.uk/local/22355
No exact match found.