The most common and most likely answer to this crossword clue is the 6 letter word AGASSI
I've seen this crossword clue in Independent
A
G
A
S
S
I
More clues leading to the result AGASSI
- Server brought over one’s drop with touch of arrogance
- Tennis champ‘s a lot of fun in Spain, I agree
- Is a big story upsetting tennis star?
- I played tennis like one with trapped wind
- Ex-champ is a legend wanting a comeback
- Dip into investment account upset ex-tennis player
- Tennis champ's a lot of fun in Spain, I agree
- Decline in savings upset former US sportsman
- Tennis player retracting one’s story
Buddy explains!

The straight part
We know that "I played tennis" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i played tennis = agassi.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.