### Clue: Gatecrash lewd independent theatre first (7)
### Answer: INTRUDE 
 ### Explanation: Definition: Gatecrash
 RUDE(lewd/obscene) **placed below**(… first, in a down clue) [ I(abbrev. for "Independent"/an election candidate belonging to no particular political party) + NT(abbrev. for the National Theatre in the UK) ].