Twist betting on rail layout (6)
I believe the answer is:
spiral
'twist' is the definition.
(I know that spiral is a more specific form of the action twist)
'betting on rail layout' is the wordplay.
'betting' becomes 'sp' ().
'on' means one lot of letters goes inside another.
'layout' is an anagram indicator (an alternative layout of the letters).
'rail' anagrammed gives 'iral'.
'sp' placed inside 'iral' is 'SPIRAL'.
(Other definitions for spiral that I've seen before include "Helical shape" , "Shape of coil or helix" , "Corkscrew shape (6)." , "Sir, pal inds in continuous loops" , "Whorl" .)