Complete the sentences: 1) A person who plays football professionally is a . 2) A person who officiates a football match is a . 3) A person who manages players is a .

Here are the answers to the questions:

1. A person who plays football professionally is a footballer (or professional footballer).
2. A person who officiates a football match is a referee.
3. A person who manages players is a manager (or coach).

Here are the completed sentences:

1. A person who plays football professionally is a $\boxed{\text{footballer}}$.
2. A person who officiates a football match is a $\boxed{\text{referee}}$.
3. A person who manages players is a $\boxed{\text{manager}}$.