There's too much liability involved in stopping shoplifters if you aren't part of the loss prevention team -- assuming you have one.
The employee could be hurt or worse.
Intervening could put other employees and customers at risk.
The employee could injure the crook and create legal concerns for the store.
If it's just shoplifting, I'd take some video for evidence and possible identification. I'd also say something to the manager (unless it's me

) and call 911.
The stores have insurance to cover theft losses. Who is going to cover the lawsuit against the store and the employee if (1) the employee made a mistake or (2) put the shoplifter in the hospital?
There's right and wrong. But then there's the crazy, stupid, litigious country in which we now live.
Ever watch the Pacino movie
And Justice for All? One case going on in the background was a purse snatcher who severely injured a woman when he grabbed her purse, but she wouldn't let go. The criminal' defense was he only wanted to rob her, but not to hurt her. Her injuries were basically her fault for not letting go of her purse.
It's a lot like that all over now.