I played cricket on sunday. have part of lower shin on inside that feels bruised to touch. severly painful to run up the stairs/ uncomfortable to walk?

May be impact: You may have been hit there and not noticed it at the time--in which case it should improve in a few days to week, quicker with cold compresses to area periodically and advil (ibuprofen) or other NSAID for pain relief. If persists beyond a week, see your dr for exam.

Tendinitis?: It could be a tendon problem, tendinitis, degeneration, or even a rupture - see a doctor.