from EDSBS:

That is the helmet of Austin Box, the Oklahoma linebacker who died in May after ingesting a fatal mix of painkillers. Teammate Travis Lewis had a freshman carry Box's helmet out to his usual spot in warmups during the Sooners' practice on Friday, and will continue the tribute throughout fall practice. His locker remains untouched, and his chair in Oklahoma's defensive meeting room will remain empty for the 2011 season.