Clue: Head of Rugby no lad's messed with? (6)
Answer: ARNOLD
Explanation: Definition: Head of Rugby no lad's messed with?
***(r no lad)** [anag:*messed with*] where R is [*head of*] R(ugby) and &lit. 
*Refers to Thomas Arnold, head of Rugby school between 1828 and 1841