Not sure exactly where you've gone wrong here, so let's map out the typical way to set this up and you can compare your system to that to spot any differences.
You should have these relationships and please note the change here for linking to records in the sport table:
Athlete::AthleteID = Activity::AthleteID (enable "allow creation of records via this relationship for Activity)
Sport::SportID = Activity::SportID
With this set up you can place a portal to Activity on your Athlete layout.
Inside this portal, you can place the Activity::SportID field and format it with a value list that displays SportID from Sport as field 1 and Sport_name as field 2. When you select a value from this value list on the bottom blank row of the portal, a new record is created in activity linked to Athelete by AthleteID. The SportID you select then links it to a record in the sport table. You can place any fields from Sport in this same portal to display additional information about the selected sport.
Thank you PhilModJunk,
I reformatted the portal and took a second look at my test view and I think the problem may have been there.
I formatted the value list to use sportID and sport_name. When a sport is selected, only the sportID shows up in the portal. Is there a way to have the sport name show instead? I have checked the "show second field only" box so that when selecting a sport, the athletes only see the sport names, but it still displays the ID after they have made their selection.
Thanks again for you help!
With the "show second fieild only" option, you can use the Pop Up menu option and then the name will show instead of the number after you exit the field. You can keep the drop down list, but put the name field from the related field next to it to display the name when you exit. You can resize the ID field to be just wide enough to display the arrow and then put it next to the name field to look like one field or you can even place the name field (with non transparent fill color) on top of the drop down field, but with behavior options selected in the inspector to deny access to this field while in browse mode. When you click on this field, the drop down list behind it will deploy.