Hi there! Yes you re right. it most likely is a hematoma or blood collection in common language. The shin has no muscles under the skin for most part and so an injury is likely to open up one of the small blood vessel there. Since it stretches the tissue around it , it causes a throbbing like pain . Most of the times it usually resolves on its own and only needs pain killers like Diclofenac or Ibuprofen(make sure you dont have any heart or kidney disease before takin them and avoid aspirin) for the pain. Sometimes they re large enough to remain for a long time and may also lead to a bacterial infection like an abscess. So my suggestion is that if it is very large then consult a surgeon or a GP and have it drained via a small incision. Healing and pain will be better that way. Hope this was helpful.