There are $38$ people in the California Baseball League (CBL). The CBL cannot start playing games until people are split into teams of exactly $9$ people (with each person in exactly one team). Moreover, there must be an even number of teams. What is the fewest number of people who must join the CBL such that the CBL can start playing games? The CBL may not revoke membership of the $38$ people already in the CBL.
1. We need to find the smallest even number of teams such that each team has exactly 9 people and the total number of people is at least 38.
2. Let \( n \) be the number of teams. Since each team has 9 people, the total number of people is \( 9n \).
3. We need \( 9n \geq 38 \) and \( n \) must be even.

4. First, solve for \( n \) in the inequality \( 9n \geq 38 \):
   \[
   n \geq \frac{38}{9} \approx 4.22
   \]
   Since \( n \) must be an integer, the smallest integer \( n \) that satisfies this inequality is \( n = 5 \).

5. However, \( n \) must also be even. The smallest even integer greater than or equal to 4.22 is \( n = 6 \).

6. If \( n = 6 \), then the total number of people is:
   \[
   9 \times 6 = 54
   \]

7. The number of additional people needed to reach 54 from 38 is:
   \[
   54 - 38 = 16
   \]

Conclusion:
The fewest number of people who must join the CBL such that the CBL can start playing games is \( \boxed{16} \).