  A moderate C1.1 class confined flare is investigated here, which occurred on
2013 September 24 at 22:56~UT, in an arch filament system close to a regular,
unipolar sunspot. Spectro-polarimetric observations from the Tenerife Infrared
Polarimeter at the 70 cm German Vacuum Tower Telescope were combined with data
from the Helioseismic Magnetic Imager and the Atmospheric Imaging Assembly to
identify the processes that triggered the flare. The legs of this arch filament
were anchored in the leading sunspot and the network flux region of opposite
polarity. The flare was driven by small-scale, flux cancellation at the weak
neutral line underlying the arch filament which resulted in two small flaring
events within an hour of the C1.1 flare. Flux cancellation was facilitated by
the moat flow from the leading sunspot wherein small-scale magnetic fragments
stream towards patches of pre-existing flux. The cancellation of flux led to
the destabilization of the arch filament which was seen as an increase in the
twist along the arch filament. The horizontal fields across the weak neutral
line decay faster which cannot prevent the filament from rising that results in
a two-ribbon flare at the neutral line. The arch filament unwinds as it rises,
but is confined by the higher, overlying fields between the two polarities of
the active region that decay much more slowly.
