Free were the first band I ever saw in big time Concert and it was a knockout.
Free were on first followed by Manfred Mann and then Deep Purple. Free's big hit was All Right Now, but since this is drums and bass thread Mr Big is the one here. I think the Bass player Andy Fraser was about 17 at the time.
There is a great live clip on YouTube but the poster of the video only allows you to watch it on YouTube. Great shots of Andy Fraser if you care to watch. If you click on the link below it will take to the YouTube site.