Hi. I am an intellectual property attorney with 8+ years of experience.
First, was there any written agreement between the theater company? If there is, then that agreement will control and this answer will be slightly different.
If there is no agreement in place you may have a joint authorship situation depending on the circumstances. As you may know, copyright
protect expressions that are fixed in a tangible medium (e.g., written into words or performed and captured on video, etc.). Therefore, there would be copyright protection in the stage play script or in the recording of the acted play but ideas that are submitted are not independently copyright protected. Looking at the stage play script, if more than one individual helped write the script then each may be considered a joint author (but each must have actually written some portion of it). To determine if a joint authorship exists, the court examine the following:
1. each author must have made a substantial and valuable contribution to the work;
2. each author must have intended that their contributions be merged into inseparable or interdependent parts of a unitary whole; and
3. each author must have contributed material to the joint work which could have been independently copyrighted.
Absent an agreement, in determining intent (#2), the court will look to see if:
a. both/all parties exercised control over the work. This is the most important factor;
b. both/all parties’ actions showed they shared the intent to be co-authors when they were creating the work, for instance by publicly stating that the work was their shared project; and
c. the audience-appeal of the work depends on the contribution of each party so that the share of each party’s contribution in the work’s success cannot be appraised.
In making a substantial and valuable contribution to a work, each author’s contribution to the joint work need not be equal. If a joint authorship is found, each author of a joint work shares an undivided interest in the entire joint work. This means that each copyright owner in a joint work may enforce the copyright in the work and exercise the benefits of the copyright.
A good case to examine which lays out this issue is Thomson v. Larson, 147 F.3d 195 (2 nd Cir. 1998) which examines the authorship of the stage play "Rent."
In sum, if you can show the above elements (i.e., that various individuals wrote the script with the intent that they be co-authors) then the joint authors are equally allowed to perform the play and dispose of any other rights in the work, as well as petition to have the copyright registration amended to reflect the other authors. If he has profited off of the copyright, you would also be able to obtain your equal portion of the profits.
Let me know if the copyright that he registered is a video recording of the play because that is a different analysis. Also, if there were any agreements in place.