Cryptic crossword clue
In mixed doubles, Rex rocks 8

The most common and most likely answer to this crossword clue is the 8 letter word BOULDERS

B
O
U
L
D
E
R
S

Buddy explains!

The straight part
We know that "rocks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case rocks = boulders.
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.

What does BOULDERS mean?

BOULDERS noun
  1. A large mass of stone detached from the surrounding land.
  2. A particle greater than 256 mm in diameter, following the Wentworth scale
  3. A large marble, in children's games.
  4. A session of bouldering; involvement in bouldering.

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