For a quadratic equation \(ax^2 + bx + c\), the product of the roots \(\alpha\) and \(\beta\) is given by:
\[
\alpha \times \beta = \frac{c}{a}
\]
For \(P(x) = 3x^2 - x - 4\), \(a = 3\), \(b = -1\), and \(c = -4\). Therefore,
\[
\alpha \times \beta = \frac{-4}{3}
\]
Thus, the correct answer is \(-\frac{1}{3}\).