C2 [ I ] to step awkwardly while walking or running and fall or begin to fall:
Running along the beach, she stumbled on a log and fell on the sand.
In the final straight Meyers stumbled, and although he didn't fall it was enough to lose him first place.
[ I usually + adv/prep ] to walk in a way that does not seem controlled:
We could hear her stumbling about/around the bedroom in the dark.
He pulled on his clothes and stumbled into the kitchen.