When a straight linear kick like the foot jab is thrown at you, one defense is the scoop. As the kick comes in you vector off the line it is traveling and catch it with the outside of the arm and hand in a scooping motion. Once scooped you can control the offending person by lifting and pushing forward. Also the leg can be pushed of to the side when released to destabilize the opponent and provide an advantageous striking position

The shin check is the primary defense against a round kick (other than avoidance). In Thai Boxing the shins slam together and each person makes the best attempt at advantageous position. It is better to take it on the shin than the softer outside of the thigh which is susceptible to damage to nerve and blood flow.