Buy if you can afford it.
It is Ireland. It’s always dark here in february afternoon. Try with other lens you have, what speed, aperture and iso you are going to use to have proper exposition.
Serious sport photographer would buy nikon d3 and nikkor 200/2.
A 300 f2.8 is a brillant lens, the advantage of the prime fixed 300 is the adjustable zoom at f2.8. For field sports this a huge advantage in that you can keep up with the action closer than the fixed 300.
have a look in the for sale section there is a 300 f2.8 nikon for sale at €1450 ish.