The best treatment for a leg hematoma involves using the "RICE" method: Rest, Ice, Compression, and Elevation. Additionally, supplementation with vitamins C and K aid in the healing process.
You can alternate between a hot compress and a cold compress. Switch after about 10 minutes. Also make sure you get enough Vitamin C and K in your diet.
Immediately after the injury, use a cold compress (ice packs) for pain and swelling. After two days, use a warm compress (even a simple a warm shower will help).