Co-Counsel
Also known as: Second-Chair Counsel
An additional lawyer or firm working alongside a case's existing counsel, rather than replacing them.
Co-counsel is a second lawyer or firm brought onto a case to work alongside existing counsel, often for a specific piece of specialized work. The Florida Bar maintains an Attorneys' Exchange where appellate practitioners advertise services including appeals, litigation strategy, second-chair work, and availability to co-counsel with other firms. The original lawyer typically keeps the client relationship and continues running the underlying case.
Bringing in co-counsel is not a sign the original lawyer is failing at the case. It is closer to how a company brings in a specialist consultant for one part of a larger project without replacing its existing team. FloridaOnAppeal.com's piece on deciding whether to bring in appellate counsel is the closest thing they've published to this question, worth reading alongside the collaborative framing here.