Shout with pain, with heart maybe leading to caution in game (6,4)
I believe the answer is:
Here is my best explanation:
'caution in game' is the definition.
'shout with pain with heart maybe leading' is the subsidiary indication.
'shout' becomes 'yell' (yelling is a kind of shouting).
'with' says to put letters next to each other.
'pain with' becomes 'ow' (I can't explain this - if you can you should give a lot more credence to this answer).
'heart maybe' becomes 'card'.
'leading' means one lot of letters go next to another.
'to' is the link.
(Other definitions for yellow card that I've seen before include "Warning leading to temporary dismissal", "Warning to footballer", "Footballer's caution", "Warning to footballers" and "With which a referee cautions player".)