Operation was planned for retrieving the wear bushing. Driller partially opened Driller side wellhead Side Outlet Valve (SOV) to drain BOP. Driller changed over from Natih line and lined up the fill up line through wellhead SOV. While making up running tool (~1.2m) and test plug at rig floor, for retrieving wear busing, the rig floor crew observed well flowing. Driller operated the Blind Shear Ram (BSR) from the Koomey unit and the well was secured. During this time a splash of water was observed from the well center, rising upto a height of approx. 5m above rotary table. As a result, the running tool and test plug assembly got caught with the split bushing and popped out to rest 1m next to well center. After performing the gas test, Assistant Driller (AD) closed the partially opened SOV.