One that tumbles, especially an acrobat or gymnast.
A drinking glass, originally with a rounded bottom.
A flat-bottomed glass having no handle, foot, or stem.
The contents of such a drinking glass.
<Other definitions removed for copyright reasons - Panjamod>
The only 2 definitions I'm very familiar with are the first two (in red). Given this knowledge, I would not recommend calling a person a "tumbler" if you mean to say that they are strong and can be knocked down. Instead, I would call them "a pillar of strength"... but it really depends on the context. Do you have a context you could give us?