Short second moment bound and Subconvexity for GL(3) $L$-functions

Let $\pi$ be a Hecke cusp form for ${\mathrm{S}\mathrm{L}}_3(\mathbb{Z})$. We bound the second moment average of $L(s,\pi )$ over a short interval to obtain the subconvexity estimate $$L(1\mathrm{/}2+it,\pi ){\ll }_{\pi ,\epsilon }(1+\mathrm{\mid }t\mathrm{\mid }{)}^{3\mathrm{/}4-1\mathrm{/}8+\epsilon }\mathrm{.}$$