I have been practicing (Shotokan) karate for quite a while now, and my technique is quite solid (according to my instructor). However, I am just not able to spar. When someone comes in with an attack, I more or less freeze up, and fumble to block (and often cannot). My movements are jerky and tentative at best. I'm wondering if this is a mental block, because I can do the individual techniques, but when it comes to putting them together and sparring someone, I just cannot. Any ideas on how to get over this/how to get better at sparring? Thanks