In a betting sport such as horse racing or boxing, the competitor for whom the odds are lowest is known as the favourite.
Can the other competitors be termed something in contrast?
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First things to come to mind are cannon fodder and also rans.
Also rans implies the race is over, but I've heard it used to describe competitors that are not expected to place.
Cannon fodder is probably a bit more mean spirited, but gives a sense of providing enough members in the race, but of lesser quality.