The most common and most likely answer to this crossword clue is the 11 letter word EXCLAMATION
I've seen this crossword clue in Independent
E
X
C
L
A
M
A
T
I
O
N
Buddy explains!
The straight part
We know that "Mark follows it/an excited cry" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case mark follows it/an excited cry = exclamation.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 EXCLAMATION mean?
EXCLAMATION noun- A loud calling or crying out, for example as in surprise, pain, grief, joy, anger, etc.
- A word expressing outcry; an interjection
- A clause type used to make an exclamatory statement: What a mess they made!; How stupid I was!
- The sign "!" by which outcry or emphatic utterance is marked.