After the discovery of the Death Star I project, the Rebel Alliance attempted to discover the identities of the contractors involved in its construction. As part of this effort they decided to hijack the Sidral II and study its cargo, in the hopes that it would reveal more about who was building the Death Star.
The capture of the freighter was undertaken by the privateer, Tuz, and a rendezvous was planned to transfer the cargo to the Rebel CR90 corvette Frazier. The operation would be protected by two R-22 Spearheads from Red Squadron, led by Keyan Farlander.
The Rebels arrived to discover that the Imperial-class Star Destroyer Immortal had already arrived and begun launching TIE/LN starfighters and TIE/sa bombers, though the Star Destroyer itself was some distance away.
The R-22s were able to hold off the TIEs while the Frazier conducted its boarding operation, retrieving the components, and both ships hyperspaced to safety.