Now that I think more about this, I remember the LP policy we had at Alberton's, which was to not physically try to stop a theft, but rather to just try to deter them by letting them know their presence is known (i.e. not even "stop stealing" but just offer good CS). The reason was twofold:
1) When I went through orientation, the manager (who was definitely over 6 feet and average build) said he went after a guy who stole something (who was definitely under 6 feet), and the next thing he knows he's waking up in the hospital. His manager told him "I think he got you with his foot."
2) Apparently a while back, a group of employees at another chain (I believe it was Walmart or Safeway, but I remember it was a big competitor) chased a thief out of the store and beat him to death. After that, most grocery stores have had very strict limits on what employees are allowed to do. Even if there isn't a lawsuit, the story in the paper "hungry man tragically dies after being beaten by angry employees" would really hurt business.