What is the best way to describe footwear that is not good for a specific activity?

The term "unsuitable" is the most fitting choice when describing footwear that is not good for a specific activity. This word directly indicates that the footwear does not meet the necessary requirements or conditions for that particular activity. It conveys a sense of lack of appropriateness in terms of design, functionality, or support needed for that specific task.

While "inappropriate" could also indicate footwear that does not fit the context well, it often carries a connotation of social norms rather than practical fitness for an activity. "Inconvenient" suggests that the footwear causes trouble or difficulty, but it does not specifically address the concept of being ill-fitted for an activity. Similarly, "impractical" implies that the footwear might not be suitable for use due to various factors like comfort or design but lacks the direct focus on fit and functionality associated with a specific activity. Thus, "unsuitable" is the strongest choice to describe footwear lacking suitability for an intended purpose.