In-Universe:
The U.S.S. Defiant is hit by a new Breen energy dampening weapon that basically cuts all power to the ship.
Production:
The first scene of the Defiant firing its pulse cannon phasers is from the third season episode 'Defiant'. This is only the second time this clip has ever been used.
This is the third version of the CGI Defiant from Digital Muse. The most telling visual element to me is the front deflector. It's supposed to be a smooth consistent curve, but in this version the top is more flat and then there is a definite 'bend' and then it curves.
