verb / noun
fumble
FUHM-buhl/ˈfʌmbl/
To handle something clumsily and lose effective control.
I fumble with my keys and drop them on the porch.

Etymology
Fumble has meant “handle clumsily” since its earliest recorded use. It may come from Old Norse falma, “to grope,” while similar Germanic words suggest a sound felt to express clumsiness.
In context
they either fumble over words or they lose their train of thought
More examples
- He fumbled the cup, spilling coffee across the counter.
- His fumble gives the other team possession of the ball.
- I fumbled the introduction and forgot our guest's name.
Forms
fumble · fumbles · fumbled · fumbling
fumbler noun — A person who handles things awkwardly.