Crossword Genius

Derby's filly, kicking out every second, is a lure (3,3)

Ross

I believe the answer is:

dry fly

'a lure' is the definition.
(dry fly is a kind of lure)

'derby's filly kicking out every second' is the wordplay.
'kicking out every second' means one should take alternating letters (every second letter removed).
'derbys'+'filly'='derbysfilly'
The alternate letters of 'derbysfilly' are 'DRY-FLY'.

'is' is the link.

(Another definition for dry fly that I've seen is " Angler knows it's a fake".)

I've seen this clue in The Guardian.
Want a hint initially instead of a full solution? Install my app