Yes, of course it is. It's competition, isn't it? This is the definition of "Sport" from thefreedictionary.com:
An activity involving physical exertion and skill that is governed by a set of rules or customs and often undertaken competitively.
Physical exertion: NASCAR drivers work out regularly to keep strong, because they are wrestling a very powerful racecar non stop for nearly four hours, in a 100+ degree cockpit. It has been known for a driver to literally lose a couple pounds from sweating during the race. It takes a LOT of stamina to do what they do.
Skill: It takes a lot of skill to hang on to a 800 horsepower heavy stock car that is on the edge of out of control every single lap. Also, running close to 190 mph, with other cars literally inches from their car. One wrong move and they are in a wreck, possibly hurting yourself or others. Sometimes its like a chess match, planning moves in advance, and reading the draft (air flowing around the car that affects the handling).