Seems like an excellent place where AI tools might be useful.
Render the image without the character.
Use img2img mode of a Diffusion imagegen tool, inpaint mask the seat area.
use a prompt like "3d semi-realistic render of a stadium with bleacher seating, bleacher seating filled with a crowd of people, mainly blue and black team color jerseys and scarfs".
play with the settings, prompt, and multiple generation cycles to get the look you want.
Then carefully combine the generated image with the original using overlay mask and color/tone/exposure correction as needed, and finally overlay the foreground character render.
Couldn't help myself, i love a challenge...:
The background could even be blurred a bit more than the original render to simulate a stronger depth of field effect... and then use masked color adjust to match the crowd's colors to the blue of his shirt:
Not bad for 15 mins work. the cutout masking for the foreground character is a bit shitm but you can render him separately and get perfectly sharp lines.
Remember the eternal truth: the background details don't matter much, the players will concentrate on the foreground unless you mess it up!