References for classical Yang-Mills theory

This is underrepresented in the literature. I have Nakahara and have looked at Frenkel (both listed in other answers) as well as many other "standard" references. The best book reference for classical YM theory that I found was Rubakov's Classical Theory of Gauge Fields.

I would add: Atiyah, Michael F. (1979), Geometry of Yang–Mills fields and then the book of the same author about gauge theories: Atiyah, Michael F. (1988e), Collected works. Vol. 5 Gauge theories

Have you tried the book "the Geometry of physics" by Th. Frankel?