The most common and most likely answer to this crossword clue is the 6 letter word SEEDED
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Buddy explains!
The straight part
We know that "Fully grown/as one of the best players" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fully grown/as one of the best players = seeded.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 SEEDED mean?
SEEDED verb- To plant or sow an area with seeds.
- To cover thinly with something scattered; to ornament with seedlike decorations.
- To start; to provide, assign or determine the initial resources for, position of, state of.
- To allocate a seeding to a competitor.
- To leave (files) available for others to download through peer-to-peer file sharing protocols (e.g. BitTorrent).
- To be qualified to compete, especially in a quarter-final, semi-final or final.
- To produce seed.
- To grow to maturity.
- To ejaculate inside the penetratee during intercourse, especially in the rectum.
- Bearing seed.
- Sown.
- Being a seed; being in a seed position
- (of a rose) Having the stamens / seeds indicated