As team leader do I have to give a reason when I am kicking someone off?

No. You don’t have to but as a team leader I believe it’s a good practice to tell a person why they’re being kicked out. But you don’t have to.

The vast majority of players know why they are removed, especially if you made the rules clear in the TEAM INFO or team chat, or periodic reminders to follow the rules.

But, to show respect to the remainder of your team, you should give a reason why they were removed.