Citizens in California are allowed to make a citizen's arrest including use of reasonable force.
1 - https://www.shouselaw.com/ca/defense/penal-code/837/#3.1
1 - https://www.shouselaw.com/ca/defense/penal-code/837/#3.1
For a misdemeanor (as the shoplifting described in this case appears to be), only if the arrested party actually committed the offense and it occurred in the arresting party’s presence (for a felony, the terms are somewhat looser.)
As the description clearly indicates that the offense did not occur in the poster’s presence and he wasn’t even aware of the offense until after using force to restrain his victim, he committed both battery and false imprisonment by violence, the latter of which is a felony offense, and the former is at a minimum a violent misdemeanor.
- https://le.alcoda.org/publications/files/CITIZENSARREST.pdf
I think this would qualify as committing the crime "in the presence" of the above commenter. Running away is part of the theft and that was done in the presence of the commenter.
Even the most liberal definition doesn’t include the arrestor being only aware of the crime after the arrest (even the looser felony citizen arrest rules require both knowledge of the offense and reasonable belief that the arrestee committed it, as well as, as in the misdemeanor case, actual guilt.)
I realize that I was over my head considering the guy was much bigger than me and I had no way of knowing if he was armed or not, but I sleep better at night knowing I did what I could to act as a decent human being.