Given boolean function $f$, let $F$ denote the unique multiaffine real polynomial representing $f$.
Sensitivity of $f$ at input $x$ is $$S_x(f) = |\{i:f(x)\neq f(x^i)\}|$$ where $x^i=x\oplus\Bbb 1_i$ where $\oplus$ is $XOR$ operation.
Sensitivity of $f$ is $$S(f)=\max_xS_x(f)$$
Is there an easy proof to show $S(f)\leq \mathsf{deg}(F)$?