Rofs,
Your question is too open ended. You need to provide more details if you want answers.
In general, I'd try to evade the blow. How I'd evade it would depend upon the angle of the blow and the range that we're at among other things. Just as with an evasion, the type of block that you'd use would also depend upon variables like the range and angle of their strike. Typically, I would not try to block a stick with my arm, except as an "oh sh*t" move. At that point, I'm trying to keep him from caving my head in and hoping to be able to close and finish him off with the one functional arm I'll have left along with whatever other weapons (natural or otherwise) I might have.
Respectfully,
Dave Fulton
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Full Contact Martial Arts Association.
"As iron sharpens iron, so one man sharpens another."