Arnett was somewhat frazzled by all of the sparks flying between the tournaments, so he decided to do something that calmed him down during the great battle between the two rival classes. Between all of the steel clashing, magic being thrown around, and the cheers of the entire crowd around him, the noise might normally be disorienting to Arnett. However, by holding a little pad and working with pencil sketches rather than his favored paint (because he'd rather not get paint on someone next to him, not because he'd get beaten up but because Orrel was only a seat away and they'd get beaten up). It wasn't quite a still life, as everything went too fast, but he was able to quickly draw up a sketch of the moment of Steven's sword and Theodora's spear colliding. He had time to work out the details, but he missed out on properly cheering due to capturing the little details.
Even off to his own corner after the battle, Arnett continued cleaning up the sketch and making the two shapeless posed figures resemble Theodora and Steven a little more. It wasn't a proper battle warmup, but it kept him from being nauseous (both from the idea of using his Arte and from the tenseness of the battle). That, to him, was the most important thing; especially when considering that the picture wasn't turning out poorly in the slightest, but some of the finer details of their anatomy were just a little off. Arnett was a master of the brush first and foremost, but practice with other tools always helped.