A piece of bad luck or a less favorable position is a disadvantage. If you are trying to run a fifty-yard dash in flip flops when everyone else has on running shoes, you'll be at a disadvantage.
It's harder to be successful when you start with a disadvantage. One kind of disadvantage is being born into a poor family — it's a struggle for a child in poverty to do well in school, attend college, or end up with a well-paying job. A disadvantage is the opposite of an advantage, a lucky or favorable circumstance. At the root of both words is the Old French avant, "at the front."
Definitions of disadvantage
noun
the quality of having an inferior or less favorable position