  We investigate the coupling constant $g_{\sigma\pi\pi}$ for the hadronic
decay $\sigma\to\pi\pi$ only using the relevant three-point function, which is
evaluated by the moving-wall source technique with a pretty good
noise-to-signal ratio. This simulation is carried out on a $40^3\times96$ MILC
gauge configuration with $N_f=2+1$ flavor of the "Asqtad" improved staggered
dynamical sea quarks at the lattice spacing $a \approx 0.09$ fm. Our estimated
value for this given MILC fine lattice gauge ensemble
$g_{\sigma\pi\pi}=2.71(42)$ GeV.
