Prop having increased intensity in game (7)
I believe the answer is:
Here is my best explanation:
'prop' is the definition.
'increased intensity in game' is the subsidiary indication.
'increased intensity' becomes 'up' (I can't justify this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'game' becomes 'sport' (I've seen this in other clues).
'up' placed into 'sport' is 'support'.
'having' is the link.
(Other definitions for support that I've seen before include "comfort", "Bear the weight of (something)", "Champion", "Help; bear", "Provide financial backing or bolster", "second", "Give assistance to", "Uphold", "Back up" and "Provide with food, clothing and shelter, or encouragement".)