The most appropriate meaning of the idiom "a slap on the wrist" is a mild punishment. The idiom comes from the idea of someone being slapped on the wrist, which is a relatively mild form of punishment. In a figurative sense, to say that someone is "getting a slap on the wrist" means that they are being punished, but not very severely.
The other options are not as accurate descriptions of the meaning of the idiom. Hitting someone on wrist is not the same as a mild punishment. Holding someone's wrist tightly is not typically associated with the idiom "a slap on the wrist." A heavy loss is not typically associated with the idiom "a slap on the wrist." | 
