No, this is not an illegal question nor is it meant to be discriminatory.  Mostly, the interviewer is trying to find out if you have common interests or something that can always be common ground between the two of you.  It is also a way for the interviewer to gage your personality and possible contributions you could make.

Give specific answers and paint a picture much like you would with any other question you are being asked during the process.  Explain why you enjoy these activities or choose to participate in them.

Describe items that you are passionate about, times you have taken on a leadership role or actively participated in a group or event. 

Be sure to include a variety of items that you do and not just focus on one.  This will show flexibility and your ability multi-task.

This is your time to make yourself stand out so be sure that your answer is as unique as you are.

Here are some examples of what to avoid:

“I spend time with my family.” 

EVERYONE spends time with their family.  Be more specific about what you do.

For example say:

Because together time is so important, every Sunday we sit down as a family and enjoy a leisurely dinner.

I cherish the time I have left with my Grandmother and I visit her on a regular basis.

“I watch TV.”  Really?  Who doesn’t?

Try to avoid using this answer.

If you must try to be more specific in regards to genre or specific actor.

For example say:

I always have been fascinated with police work and I am a huge fan of Crime shows, specifically I really enjoy all the CSI shows.

“I’m a sports fan.”  Again everyone likes at one team.

Instead, expand on what sports, what time.

I was born and raised in Chicago so I love our local teams! I like follow the Bears, Bulls, Hawks and Cubs.  I try to attend games and catch some games on TV especially the Blackhawks.

“I like to read.”  We all read, whether it’s the newspaper, our e-mail or social media.

Much like the TV answer you should phrase it specifically:

History was my favorite subject growing up and I am a big fan of civil war history novels. I enjoy reading fiction stories based during that time period.

“I play sports.” 

What kind of sports?  Are you on a team?

Be more specific, what type of sport, maybe what position.  Talk about your involvement in a league or on a team.

For example:

I played basketball in High School and still play in a winter indoor league.  Last year, I was our team statistician.

“I volunteer at my Catholic church.”

“I volunteered on a Democratic congressional campaign.”

“I am Vice President of the Silver Ladies Luncheon Committee.”

Though these are great examples of specific, more unique activities however these answers could lead to discrimination.

Be vague when it comes to an answer about religion, specific political party affiliation, ethnic groups, sexual orientation or age.

Better ways to say the same thing:

I volunteer with a religious organization by helping to get non-active members more involved.

I was a volunteer with a local political campaign; I made calls to potential voters.

I am the Vice President of a social group that meets regularly for lunch to discuss relevant topics.

Here are some other great examples of how to answer what you do in your free time:

“I love to learn about different cultures, and I travel internationally as much as possible.”

“I find that running clears my head and I like to run at least 3 times per week.”

“I really enjoy nature and I like to hike or walk in the nature preserves by my house.”

“I have a huge heart for animals and I volunteer with a dog rescue group.”

“I like adventure and the feeling of the wind blowing on my face so I ride my motorcycle.”

“I love to work with my hands and I enjoy doing various home repair tasks.”

“I respect the craftsmanship of older furniture and go antiquing all over.”

“I like to use my creative side so I knit and crochet items for me and friends.”

Our spare time is unique to all of us.  During an interview this is a perfect time to let your personality shine through.  Again, be specific about the activities and avoid giving answers that could be discriminatory.  Interviewers will remember either what’s unique to you or something you have in common, this will help when they are trying to make their hiring decision.