  The electromagnetic tensor for inclusive electron scattering off the pion,
($W^{\mu\nu}$), for momentum transfers such that $q^+=0$, ($q^+=q^0+q^3$) is
shown to obey a sum-rule for the component $W^{++}$. From this sum-rule, one
can define the quark-antiquark correlation function in the pion, which
characterizes the transverse distance distribution between the quark and
antiquark in the light-front pion wave-function. Within the realistic models of
the relativistic pion wave function (including instanton vacuum inspired wave
function) it is shown that the value of the two-quark correlation radius
($r_{q\bar q}$) is near twice the pion electromagnetic radius ($r_{\pi}$),
where $r_{\pi} \approx 2/3$ fm. We also define the correlation length
$l_{corr}$ where the two - particle correlation have an extremum. The
estimation of $l_{corr}\approx 0.3 - 0.5$ fm is very close to estimations from
instanton models of QCD vacuum. It is also shown that the above correlation is
very sensitive to the pion light-front wave-function models.
