Way of playing with toy? Cheers up breaking it (6)
I believe the answer is:
legato
'way of playing' is the definition.
(musical term)
'toy? cheers up breaking it' is the wordplay.
'toy?' becomes 'lego' (I've seen this before).
'cheers' becomes 'ta' (both can mean thank you).
'up' says the letters should be written backwards (in down clue: letters go upwards).
'breaking it' is an insertion indicator (inserted letters break in).
'ta' backwards is 'at'.
'lego' enclosing 'at' is 'LEGATO'.
'with' acts as a link.
(Other definitions for legato that I've seen before include "Smoothly (musical)" , "Don't play roughly" , "Smoothly flowing in style" , "scored smoothly" , "Smooth, flowing (mus.)" .)