USC football head coach Clay Helton has reportedly fired the bulk of the Trojan defensive coaching staff, with only linebackers coach Peter Sirmon remaining in place.

UPDATE: USC has confirmed the firing of Justin Wilcox, Keith Heyward, Bob Connelly and Chris Wilson. Tee Martin, Marques Tuiasosopo, Peter Sirmon, Johnny Nansen and Ivan Lewis have been retained.

The firings include defensive coordinator Justin Wilcox, defensive backs coach Keith Heyward and defensive line coach Chris Wilson among others, according to a variety of media reports on Twitter.

RELATED: 5 Reasons USC’s Hiring of Clay Helton Could Be Great

Source tells me much of #USC‘s staff has been let go. Hearing only Sirmons (LB), Tuiasosopo (QB/TE) and Martin (WR) have been retained. — Adam Maya (@AdamJMaya) December 6, 2015

Per source, USC coaches Keith Heyward, DB coach and Chris Wilson, defensive line, are dismissed. — Lisa Horne (@LisaHorne) December 7, 2015

This is ($) but Heyward definitely gone, Martin, Sirmon and Tuiasosopo definitely safe. https://t.co/KNfZSbYrla — Ryan Abraham (@insidetroy) December 7, 2015

Almost as soon as it was announced that Helton had been the hired as the permanent head coach at USC, reports of massive staff changes followed. The only question was when those changes would be made and how many coaches would be let go.

Now it appears that all of USC’s staff except for wide receivers coach Tee Martin, quarterbacks coach Marques Tuiasosopo and linebackers coach Peter Sirmon are due to depart.

Though it appears certain that USC’s defensive coaching staff has been axed, there remain questions about the status of offensive coaches such as offensive line coach Bob Connelly and running backs coach and special teams coordinator Johnny Nansen.

The Trojans were downed in the Pac-12 Championship Game on Saturday by Stanford, 41-22. As Christian McCaffrey gashed the USC defense, the possibility of Wilcox keeping his job became more and more bleak.

Considering the way USC’s defensive backs were abused against Oregon, the dismissal of Heyward comes as no surprise as well. He will not coach the Trojans for the bowl game, according to Gary Klein of the LA Times.

Wilson’s status was complicated by the presence of his son, Caleb, as a walk-on tight end. However, the Trojan defensive line was not able to produce enough this season to save his job.

Offensively, calls for change have not been as loud, but are perhaps as necessary. Connelly’s arrival saw the Trojan offensive line take a step back from last season, though injuries to Max Tuerk and Toa Lobendahn did not help that situation. Such an excuse does not appear to have spared Connelly from the ax.

If indeed Nansen has been let go, his downfall may have been on special teams. USC’s running backs have thrived this season, but the Trojan special teams unit has been a liability except for Adoree’ Jackson’s pair of punt return touchdowns.

Meanwhile, the retention of Martin, Tuiasosopo and Sirmon comes as no surprise. Martin is a hot commodity in the coaching community as an up-and-coming position coach and top tier recruiter. Tuiasosopo also has a reputation for being able to bring in big recruits while Sirmon’s work with the USC linebackers has been lauded.

Lindsey Thiry of the LA Times reports that strength and conditioning coach Ivan Lewis is not among those who have been fired, though interest from other options could compete with Helton’s desire to retain him.