If you do not want raw edges showing on your jersey you will need to turn under the edge of the tear. Use an iron set on the proper temp to just fold it under. Or turn it under with your fingers and pin in place. Next take a spoon or something smooth and flat but not sharp, lay the fabric on a hard surface and rub the fabric fold you just created. This will essentially press the seam but you won't end up with burnt fingers.
Depending on the sevarity of the cut you will end up with a slight gap between the folded edges. Do not try to pull the cut shut too much as this will make the mend pucker. Lay a piece of cardboard or something of that nature inside the shirt. Position a piece of matching fabric (at least matching in color if you don't want to see the contrast) on the cardboard under the cut. Pin into place around the cut and the edge of the patch.
With thread that matches the jersey's color sew down the edges of the cut to the new layer of fabric. There are several different stitches you could use. One is to use a series of short stitches going from top to bottom along the line of the edge - running stitch. Another is a blind hem used in quilt aplique (or in this case reverse aplique) where you run a very short stitch through the very edge of the fold of the jersey then go down through the patch material with a tiny stitch, over just a little under the fold and come back up to the top. Reapeating that the whole way around. Or you can use a back stitch all around the fold. Just stay close to the edge and catch the part that you turned under.
Next using a running stitch or back stitch and sew around the edges of the patch.
Try not to make the patch slightly larger than the cut, perhaps half an inch on each side, not much more. You do not need to fold the edges of the patch as they are on the inside and unseen.
It may sound complicated but it's very easy. Try looking on youtube or for pictures of the type of stitches I described.
Good luck.
H.R.
February 2010