The most common and most likely answer to this crossword clue is the 4 letter word DOPE
I've seen this crossword clue in The Times
D
O
P
E
More clues leading to the result DOPE
- American first-class train?
- Perform sport, or cheat thereat?
- Take exercise? Stupid person!
- Party leaders in politics expect information
- Goofy type providing information
- Partake in exercise, fool!
- Drugs provided by jerks after party
- Information given by party training
- Maybe work out the facts?
- Take exercise, a drug
Buddy explains!

The straight part
We know that "fool" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case fool = dope.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 DOPE mean?
DOPE noun- Any viscous liquid or paste, such as a lubricant, used in preparing a surface.
- An absorbent material used to hold a liquid.
- Any varnish used to coat a part, such as an airplane wing or a hot-air balloon in order to waterproof, strengthen, etc.
- Any illicit or narcotic drug that produces euphoria or satisfies an addiction; particularly heroin.
- Information, usually from an inside source, originally in horse racing and other sports.
- (fireams) Ballistic data on previously fired rounds, used to calculate the required hold over a target.
- A stupid person.
- Dessert topping.
- To affect with drugs.
- To treat with dope (lubricant, etc.).
- To add a dopant such as arsenic to (a pure semiconductor such as silicon).
- To use drugs; especially, to use prohibited performance-enhancing drugs in sporting competitions.
- To judge or guess; to predict the result of.
- Amazing.