The most common and most likely answer to this crossword clue is the 4 letter word PROP
I've seen this crossword clue in Financial Times
P
R
O
P
More clues leading to the result PROP
Buddy explains!

The straight part
We know that "Lean/forward" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lean/forward = prop.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 PROP mean?
PROP noun- An object placed against or under another, to support it; anything that supports.
- The player on either side of the hooker in a scrum.
- One of the seashells in the game of props.
- (sometimes figurative) To support or shore up something.
- To play rugby in the prop position
- (usually with "up" - see prop up) To position the feet of (a person) while sitting, lying down, or reclining so that the knees are elevated at a higher level.
- An item placed on a stage or set to create a scene or scenario in which actors perform.
- An item placed within an advertisement in order to suggest a style of living etc.
- The propeller of an aircraft.
- To manually start the engine of a propeller-driven aircraft with no electric starter by pulling vigorously on one of the propeller blades using the hands, so that the propeller can catch ignition.
- A proposition, especially on an election-day ballot.
- Propellant