underdog
An old expression from the Australian bush. Before sawmills made their appearance, felled logs were dragged to a saw-pit and cut lengthwise into planks by two men using a cross-cut saw, a mean beast of a thing up to 10 feet long. One man would stand on top of the log and push down, and the man underneath standing in the pit - the underdog - would push the saw up.

A rotten job, with sawdust in your eyes all day and really hard work compared to the top dog who just had to push the saw down. The boss never saw how hard this man worked, so he was less likely to get a better job, a pay rise or be noticed at all.

Now an underdog is someone - or something which is going to struggle against superior odds to win a contest.
The new Vegetarians Party will always be the underdog in Texan elections.