  The $\gamma$-ray flare of PKS 1222+216, observed in June 2010, is interpreted
as an outcome of jet dynamics at recollimation zone. We obtained the
$\gamma$-ray light-curves in three different energy bands, namely, 100--300
MeV, 300 MeV--1 GeV and 1--3 GeV from observations by the \emph{Fermi} Large
Area Telescope (LAT). We also use the \emph{Swift}--XRT flux from 0.3--10 keV
obtained from archival data. We supplement these with the 0.07--0.4 TeV
observations with MAGIC telescope, available in the literature. The detection
of source at very high energy (VHE, $E>100$ GeV) with a differential photon
spectral index of $2.7\pm0.3$ and the rapid variability associated with it
suggests that the emission arises from a compact region located beyond the
broad line emitting region. The plausible $\gamma$-ray emission mechanism can
then be inverse Compton scattering of IR photons from obscuring torus. Further,
the decay time of LAT flare cannot be explained by considering simple radiative
loss mechanisms. Hence, to interpret the LAT light curves, we develop a model
where the broadband emission originates from a compact region, arising
plausibly from the compression of jet matter at the recollimation zone. The
flare is then expressed as an outcome of jet deceleration probably associated
with this focusing effect. The parameters of the model are further constrained
by reproducing the broadband spectral energy distribution of the source
obtained during the flare episode. Our study suggests that the particle energy
density exceeds magnetic energy density by a large factor which in turn may
cause rapid expansion of the emission region. However, near equipartition can
be achieved towards the end of LAT flare during which the compact emission
region would have expanded to the size of jet cross-section.
