One likely to lose is urged on anyhow, maintaining decorum initially (8)
I believe the answer is:
Here is my best explanation:
'one likely to lose' is the definition.
'urged on anyhow maintaining decorum initially' is the wordplay.
'anyhow' indicates an anagram.
'maintaining' indicates putting letters inside.
'initially' suggests taking the first letters.
The initial letter of 'decorum' is 'd'.
'urgedon' with letters rearranged gives 'underog'.
'underog' going around 'd' is 'UNDERDOG'.
'is' is the link.
(Other definitions for underdog that I've seen before include "Competitor expected to lose", "One with little status", "One thought to have little chance of winning", "Likely loser", "outsider", "Probable failure", "Canine expected to lose?", "Unlikely Victor could be", "Such is unlikely to succeed" and "Lower-rated competitor".)