Don't force the issue. If he doesn't want to eat, just calmly say, okay!, finish with breatfeeding or formula till he's full, and try solids again later. Or don't try later. He doesn't need anything but breastmilk or formula till he's one.
The main thing is to keep solids mealtimes pleasant and stress-free for him. Otherwise, you're setting yourself up for battles of wills later - severe control issues. Go ahead and let him spit out his food. Let him bang his spoon, splatter stuff, rub it around on his high chair tray...it's all play, and play is how they learn. It's also how they become familiar with a new experience, which can be a little scary for them. If it gets too messy/stressful for you at any point, just end the feeding calmly and fill that tummy the old tried and true way.
Also, he might be rejecting new textures and especially new consistencies (thicker, coarser). Be especially careful to only very gradually increase the thickness of his foods, or he will, out of fear of choking, reject them - and develop that nuisance, texture aversions, which can stick throughout childhood, even for life, with some foods.
Feed him when he's a little hungry but not very hungry. I'm concerned to read advice about waiting till a baby is very hungry before feeding him/her - and especially concerned about refusing food from a frantic baby to try to discipline. Babies need to eat when they're hungry (and dehydrated - remember, they're trying to feed to slake thirst, too), and it's just plain cruel to let them get so hungry and thirsty just for our convenience. For a baby, it feels like life or death to have such a need go unfulfilled. I'm sure it can also cause a baby to distrust a parent who is supposed to meet all of their fundamental life needs. But not withholding food is also important for engendering a long-term healthy attitude toward food and mealtimes: if you try to feed a baby solids when he's very hungry, he'll get so desperate, and easily frustrated with this new process - spoon, high chair, unfamiliar stuff - Mom or Dad will get frustrated, baby is feeling very frazzled with hunger, etc. You can see how this goes. It can also lead to compulsive- and stress eating later in life.
Just relax! He's only six months. No big deal! Just have fun with it and keep lots of washcloths handy.
For really great advice on feeding read Super Baby Food by Ruth Yaron - millions of copies sold for a reason!!
L.