Go over the reason plays show promise (5,4,5)
I believe the answer is:
cross ones heart
'promise' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'go over the reason plays' is the wordplay.
'go over' becomes 'cross' (to cross over).
'plays' indicates anagramming the letters.
'the'+'reason'='thereason'
'thereason' anagrammed gives 'onesheart'.
'cross'+'onesheart'='CROSS ONES HEART'
'show' acts as a link.
Can you help me to learn more?
(Other definitions for cross ones heart that I've seen before include "to make solemn pledge" , "Make assertion of sincerity" , "Indicate sincerity" .)