Contradict is to speak/act against what was earlier said/done.
In usage, always, A contradicts B. So there always has to be a subject and an object.
It can either be thoughts or actions:
e.g of thought : Gavin decided one day that he will never trust Siva. But contradicting himself, he went ahead and believed Siva the very next day
e.g. of Action : Gavin decided that he will never play football again. The very next day he was found playing football.
e.g. While arguing against the topic in a debate, Gavin was soon found to be contradicting himself by speaking in favour of the topic.