Go to http://www.fatcatpatterns.com/freepatterns.html she has loads of free patterns that would work great. Made a few myself

You could find sporting fabric for all sports or his favorite sport, then a simple 9 patch alternating with a square, either plain, the size of the 9-patch, or you could snowball the square. I made my DS an Irish Chain quilt in black and bright blue when he was about 11, and the quilt followed him every time he left home and every time he returned (I had boomerang kids, they kept returning- LOL). You could do an Irish chain in 2 colors, then use sports material on the back of t he quilt.

there are many patterns out there that look good with sports prints. you could also add either his favorite teams colors or fabric. or you could just do his favorite colors and be done.

My first thought is the easy quilt pattern that has the rectangles with shadows pattern. You could use various sport themed fabrics for the "floating" rectangles, a dark gray or black for the shadows and a lighter grey or coordinating blue as the background. There is a MSQ video on this classic pattern. It is a clean, modern look that would be great for a teen.

i did snowball and nine patch for my grandson and he loves it... just use fabrics in his favorite colors

I love, love, love your quilt. The colors with black are absolutely stunning.

Loved them all!

I used the BQ pattern and appliqued a different sport in each large block. My grandson really liked it and then made a baseball print pillowcase to compliment it!

Being a preteen boy, he may change the sport he is most interested in - a couple times! Why not make one that represents several of the 'big' sports.

I made both of my sons quilts of their favorite colors when they started college. They still have these quilts today-ten and twelve years later. One was made of red/blue/gray flannels which I have mended many times over the past ten years. The other was various shades of orange, purples and red batiks which is now a couch quilt in his apartment. Their wives are more tolerant of them being around the house because they are NOT themed. It wasn't planned this way but I am glad it ended up like that.