Unfortunately, the functionality is not currently available. I have created a feature request so we can consider it at some point. You can track it on the following link - Chart: Add Overflow support for Legend with Horizontal Orientation
. I have added some points to your account for the suggestion.
In the meantime, you can consider using vertical orientation for the RadLegend.
Do you want to have your say when we set our development plans?
Do you want to know when a feature you care about is added or when a bug fixed?
Telerik Feedback Portal
and vote to affect the priority of the items