Here's a breakdown:
* "Although" is a subordinating conjunction, which means it introduces a dependent clause that needs an independent clause to make a complete sentence.
* "you thoroughly enjoyed play" is a dependent clause because it doesn't express a complete thought on its own. It raises the question: "Enjoyed what?"
To fix the fragment, you need to add an independent clause that completes the thought. Here are a few possibilities:
* "Although you thoroughly enjoyed play, you knew it was time to go home."
* "Although you thoroughly enjoyed play, you were exhausted."
* "Although you thoroughly enjoyed play, the game was cancelled."