Employees who don’t have a lot to do will inevitably become bored which can then lead to frustration. It might cause them to make careless actions or resent the few tasks that they do need to do. The law is not entirely clear on what will happen if an employee injured themselves if they were goofing off or playing a game when there was nothing else to do, but it is best practice to keep them as engaged as possible. If not you could be in a war with a situation you don’t have time for.
Consider a case where laborers were on the job and found an old bowling bowl in Pennsylvania. One thing led to another when the bowling ball smashed and the shard hit someone’s eye. Or consider an employee who wanted to chill out in an air conditioned truck in South Dakota and convinced his co-worker to leave the vehicle for a while. Once the co-worker came back, the sufficiently chilled man decided to dodge his co-workers potential physical punishments by running away. When he tripped, he claimed workers comp for this.
Judges both awarded people compensation in these cases, though the bowling ball case was overturned by the workers compensation board. The bowling ball case had a mitigating factor of a supervisor who did tell the employees to stop messing around with the bowl before the injury had occurred. Had that supervisor not been there, the courts generally do not see a momentary mistake as a means to deny care for the employee.
Whether or not you agree with these decisions isn’t really the point. You need to ensure that employees do have productive tasks and that there are specific rules on horseplay. Busy employees not only are less likely to find trouble, but are also more likely to take pride in what they’re doing. This is not to say that people can’t blow off steam and have fun because sometimes that’s necessary in the workplace too. However, there needs to be guidelines in place as to what is and isn’t acceptable. If you witness employees being just a little careless on the job, then it can’t be ignored.
The bottom line here is that even you dispute and win a case over an idle employees hijinks, it can eat up a lot of time and money. Days should be structured with deadlines when necessary. When employees are waiting for machinery or certain processes to be complete, there should be a list of approved activities that they can do. Don’t try to limit their freedom entirely though as this will cause further annoyance and resentment.