Newbie here with question

Hello. I currently own the Canon EF 100-300mm f4.5-5.6 USM lens and am considering purchasing a Canon EF 100-400mm f4.5-5.6 L IS USM lens. Other than the image stabilization, cost and increased 100mm on the "L" lens, is this the better of the two lenses for shooting outdoor sports action? Thank you for your valued input!

Best Regards,
Cyclop

Welcome to PotN, Cyclops.

Well some would say that 400 might be a touch too close for sports (depends on what sports you're shooting of course!), but at least you have the option of going to 400mm if the needs arises (like with Baseball or such).

I've never used the 100-300, so can't comment on it's quality, but the 100-400 is a great lens, and the IS helps especially at 400mm.
And 400mm @ 5.6 will give you more bokeh (aperture blades being constant) than 300mm @ 5.6
Bokeh is God for sports IMO.

i think the 100-400 will be better for sports than what you have, but if you are buying this lens specifically for sports, I'd think about getting somethign a little faster--either a fixed f/4 lens, or even better would be f/2.8

welcome to POTN and do some searches. I'm sure you'll find waaaay more information that you need.