I think I should make the difference between what actually causes physical shock and what you’re suggesting, which is that extreme pain can trigger it,“Circulatory shock, commonly known simply as shock, is a life-threatening medical condition that occurs due to inadequate substrate for aerobic cellular respiration.” (Wikipedia, but it has a source on the statement, so I trust it). The primary causes of shock include inadequate circulating volume (bloodloss or if you like fancy words hypovolemia ), ineffective heart (cardiogenic shock), or septic shock (infection causing mass amounts of hystamine production causing intense vasodilation)
Acute stress reaction is likely closer to what you’re thinking, but it’s still a longshot. Pain itself is only a sign of something getting screwed up in the body. Frankly, it’s why we have pain receptors in the first place. What should probably happen is a loss of strength, and possibly loss of consciousness. Otherwise, paralysis might be possible, but I just don’t know enough to make that determination.
Also, adrenaline is often released in a combat situation while facilitating the fight or flight response, which seriously impedes pain’s influence in combat situations.