You just bought that Jersey for your favorite sports star, or maybe they threw it to you during the game. Now you want to protect and display it.
Take plywood and cut with saw to inside .5 inch longer and .5 inch wider than the inside width/length of frame.
Now, cut two strips 1 inch wide and the same length as the plywood rectangle
Then use finishing nails to nail strips to the long sides of the plywood rectangle.
Cut two more strips to fit along top and bottom of the plywood rectangle
Attach jersey to inside of the plywood "box" you just made. Use desired method.
Cut Plexiglas to fit on the inside of frame. Then glue it into place. Make sure to cut it large enough the glue can be hidden.
Now Glue or Use nails to attach the frame to the box. If you measured it correctly you will have a box that is hidden from view thru the frame.