The most common and most likely answer to this crossword clue is the 6 letter word BRIERS
I've seen this crossword clue in Independent
B
R
I
E
R
S
More clues leading to the result BRIERS
Buddy explains!
The straight part
We know that "old sitcom actor" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case old sitcom actor = briers.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 BRIERS mean?
BRIERS noun- Any of many plants with thorny stems growing in dense clusters, such as many in the Rosa, Rubus, and Smilax genera.
- Anything sharp or unpleasant to the feelings.
- The white heath, Erica arborea, a thorny Mediterranean shrub.
- A pipe for smoking, made from the roots of that shrub.