The most common and most likely answer to this crossword clue is the 6 plus 7 letter word CENTRE FORWARD
C
E
N
T
R
E
F
O
R
W
A
R
D
Buddy explains!
The straight part
We know that "One expected to attack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one expected to attack = centre forward.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.