### Clue: Flat's very loud during racing event on screen (3-12)
### Answer: NON-EFFERVESCENT 
 ### Explanation: Definition: Flat
 FF(abbrev. for the musical direction, fortissimo, to play loudly) **contained in**(during) **anagram of**(racing) EVENT ON SCREEN.
Answer: If I put on my pedant's hat, I'd say that "non-effervescent" is to be (or is expected to be) without bubbles right from the start, as with still as opposed to sparkling water, whereas "flat" is to have lost its bubbles or is expected to, but does not, have bubbles, as with flat champagne.