Personally the glue is a waste as it leaves residue, so if you want to move a patch to your right arm/ or left arm shoulder from your front pocket, then sticky residue is left behind.
Someone said the two sided adhesive tape works well. I'm going to give that a shot. And the same applies to the velcro as it leaves a residue on the shirt. I've ruined a jacket and several shirts because that residue is impossible to remove. There's got to be another way.
Although one guy says he sews onto the back of his umpire patch, a tiny bit of cloth that he buys from "Michael's," & leaves enough cloth loose, so he can attach tiny snaps through the cloth, and then he can snap it on to the shirt. I haven't tried it, but it looked fine when I saw him wearing the patch. I'm still going to try the double-adhesive tape first.
Bob
San Dimas, Calif.