  Light bridges (LBs) are relatively bright structures that divide sunspot
umbrae into two or more parts. Chromospheric LBs are known to be associated
with various activities including fan-shaped jet-like ejections and
brightenings. Although magnetic reconnection is frequently suggested to be
responsible for such activities, not many studies present firm evidence to
support the scenario. We carry out magnetic field measurements and imaging
spectroscopy of a LB where fan-shaped jet-like ejections occur with co-spatial
brightenings at their footpoints. We study LB fine structure and magnetic field
changes using TiO images, Near-InfraRed Imaging Spectropolarimeter, and Halpha
data taken by the 1.6~m Goode Solar Telescope. We detect magnetic flux
emergence in the LB that is of opposite polarity to that of the sunspot. The
new magnetic flux cancels with the pre-existing flux at a rate of 5.6x10^18
Mx/hr. Both the recurrent jet-like ejections and their base brightenings are
initiated at the vicinity of the magnetic flux cancellation, and show apparent
horizontal extension along the LB at a projected speed of up to 18.4km/s to
form a fan-shaped appearance. Based on these observations, we suggest that the
fan-shaped ejections may have resulted from slipping reconnection between the
new flux emerging in the LB and the ambient sunspot field.
