Mark, my son, turned to run, losing time (6)
I believe the answer is:
symbol
'mark' is the definition.
(I've seen this before)
'son turned to run losing time' is the wordplay.
'son' becomes 'mys' (I can't explain this - if you can you should give a lot more credence to this answer).
'turned' is a reversal indicator.
'to run' becomes 'bolt'.
'losing' indicates named letters should be taken away.
'time' becomes 't'.
'mys' reversed gives 'sym'.
'bolt' with 't' taken away is 'bol'.
'sym'+'bol'='SYMBOL'
'my' is the link.
This may not be correct. It may be part of another bit of the clue.
(Other definitions for symbol that I've seen before include "Emblem or sign" , "Something representative" , "Representative sign" , "Meaningful mark" , "Something that stands for something else" .)