For a few days my cat have been sceard of everyone and if you tried to pick him up he would scratch and bite.after a while he started to poo every where in the house even if the litter tray was right next to him. After a day my mum said that he is not allowed in the house anymore and that he will have to sleep outside and that she will not take him to the vet because it costs too much money.
Is that a mental disorder?
How can I help him?

Alex5500,
If a cat behaves the way you have described, then she/he might be traumatised. Your cat is telling you that something is not in order. I must say, if you are a cat owner, you need to have the financial means to take care of your cat in any case! If your mother is not willing to pay for a vet, then you really shouldn't have gotten your cat in the first place.
There are cat psychologists who know why cats do things as you described. Try to find a website or a ask at a shelter where you could go for help.