First of all, it sounds like something may have happened during his time playing soccer last fall that lowered his confidence. I think at his age, he should not be committed to any structured sport. He should be exposed to the different sports, but just not in a particular sport class. Perhaps you can put him in a tumbling group or some sort of exploratory movement class that simply introduces children to different movements while helping them to strengthen and develop gross motor skills like running, kicking, throwing a ball. Something that just focuses on having fun performing different movements.
Another idea is instead of playing a game like soccer or basketball where you have to kick or throw the ball in or at a particular target, play something like kickball or catch with a light-weight ball like a beach ball.
Get creative to help build his confidence. Try buying 2 or 3 hula hoops and a few bean bags (you can make the bean bags using some of your child's old socks and some beans, rice, or old fashioned unpopped) to create a game. Take the hula hoops put them in front of your son (put them somewhat close to him to start. Have him try to toss the bean bags into the hula hoops. After he has thrown all of the bean bags, move the hula hoops a little further away. Keep moving the hula hoops further and further away each time. This game may help boost his confidence. It may also spark him to challenge himself to see how far he can move the hula hoops, thus making him less afraid to try.
Also, Make sure you and your family set a good example. Is there someone in the home that gives up when things don't go their way? If there is, address what you observe and stress the importance in setting a good example when it comes to this issue as well as the importance of not giving up.
Sorry I wrote so much. There's more that I wanted to say, but I hope this info will be a help to you.
P.S. If you want other creative play ideas, please feel free to send me a message.