Clue: Withdrawal of soldiers on exercises, all cut short (6)
Answer: REPEAL
Explanation: Definition: Withdrawal
 RE(abbrev. for the Royal Engineers, soldiers in the British Army) **placed above**(on, in a down clue) PE(abbrev. for "physical education", instruction in physical exercise) + "all" **minus ****its last letter**(cut short).
Defn: A formal …/a revocation of, say, a law.