The most common and most likely answer to this crossword clue is the 8 letter word GORINESS
I've seen this crossword clue in The Daily Telegraph
G
O
R
I
N
E
S
S
Buddy explains!

The straight part
We know that "Awful quality of Colosseum performance" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case awful quality of colosseum performance = goriness.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.