The most common and most likely answer to this crossword clue is the 7 plus 10 letter word PRESENT PARTICIPLE
I've seen this crossword clue in The Times
P
R
E
S
E
N
T
P
A
R
T
I
C
I
P
L
E
Buddy explains!
The straight part
We know that "E.g. coming" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case e.g. coming = present participle.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.