Final answer:
The main safety concern with 'teak surfing' is propeller injuries, which occur when individuals are too close to the boat's propeller while engaging in the activity.
Step-by-step explanation:
'Teak surfing' is an activity that poses various safety risks, and one of the main safety concerns involving this activity is propeller injuries. This activity involves holding onto the swim platform or transom of a moving boat and then letting go to body surf on the boat's wake. The proximity to the boat's propeller while 'teak surfing' is extremely dangerous as it can lead to severe injuries or even fatalities. In the state of Nebraska, as in many other places, 'teak surfing' is illegal due to the high risk it poses to individuals engaging in the activity.