Require any answer from list of answers to continue

I am building registration form for a camp we are running.  I want to make the camp free for athletes that attended a precious camp we ran.  

Therefor on the form I would like the athlete to enter his last name and require it to match a name from a list I provide, in order to continue.  Is this possible?

Basically, you need to compare two fields values, the one entered in a text box with the values listed in another field. 

What you could do is to list the pre-defined values in a drop down, then ask for the needed name in a text box field. With conditions you will be able to compare both values, but they must be the same in order  to trigger the conditions, and also you cannot compare a text box value with a drop down so you would need to capture the value from the drop down in order to compare both values. 

Here's a sample form that works similar to what you need: https://form.jotform.com/70514691309961 

Here're the steps to achieve that, first add a text box field where you will ask for the submitter's name, it must be a text box since using a name field will not trigger the condition. Add also a drop down where you will list the pre-defined names you have and add a second text box where you will capture the drop down's selected value. 

Once the field are added you need to do the conditions to copy the fields values and compare them. 

With this condition you will copy the field's value entered in the name text box field and insert it into the drop down, if there's a similar value then the drop down will change its value to that option: 

Then add the condition to copy the drop down selected value to the second text box:

You can then compare both text boxes values, on my example, I show a text if both values are the same, you could change it to require other fields or the action you need on your form: 

Please give it a try, if you want to clone my form this guide will help you: https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL 

If you have any question, let us know.