The most common and most likely answer to this crossword clue is the 6 letter word RARING
I've seen this crossword clue in The Times
R
A
R
I
N
G
More clues leading to the result RARING
Buddy explains!

The straight part
We know that "Eager" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case eager = raring.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 RARING mean?
RARING verb- To rear, rise up, start backwards.
- To rear, bring up, raise.
- Eager.