I think this is a common issue for this age. I think it could be exaggerated for a child with SPD though if they have delays where they feel like they are always coming in last or losing. And of course kids with SPD have more trouble with emotional regulation which could make it harder for him to recover (hence the hiding in the tent) What we do is try to be silly about it. Like when we play checkers and she jumps me I'll say "STINK" and slap my forehead dramatically. There's some really good tips for a child who has a hard time losing in the book "Playful Parenting" by Lawrence Cohen too. He talks about have times of the parent being silly and pretending to make lots of mistakes or do everything wrong as kind of a theraputic way to play with them and help them cope with this, just be careful not to do it in a way that's making fun of the child of course. My child is only 5 but I have to say I do make sure she wins at least half the time (but I would never let her win all the time).