Here's why:
* Lame (adjective): Means impaired or injured, often referring to a limping gait.
* Lame (noun): This is a less common usage, but it can refer to a specific walk or step that is awkward or clumsy.
So, depending on the context, "lame" can be used to describe both the physical condition of a walk or step, and the quality of the walk or step itself.