Here are a few options for a WordPress post tag description for “直線球” (Straight Ball) in Traditional Chinese, varying in style and length:

**Option 1 (Concise & General):**

> 直線球 (Zhíxiàn qiú): 一種在棒球或壘球中，沿直線飛行的投球類型。 (Zhíxiàn qiú (Straight Ball): A type of pitch in baseball or softball that travels in a straight line.)

* **Explanation:** Short, direct, and explains the term in English, good for accessibility.

**Option 2 (Slightly More Detail):**

> 直線球 (Zhíxiàn qiú): 棒球或壘球中，速度快且路徑相對筆直的投球。投球者通常以此球種來挑戰打者，或是作為其他變化球的搭配。 (Zhíxiàn qiú (Straight Ball): In baseball or softball, a pitch that is fast and has a relatively straight trajectory. Pitchers often use this pitch to challenge batters or as a setup for other breaking pitches.)

* **Explanation:** Offers a little more context about strategy.

**Option 3 (Emphasis on Usage and Significance):**

> 直線球 (Zhíxiàn qiú): 棒球投球的基本球種，也是各種變化球的基礎。 投球時，球以直線軌跡快速飛向打者，考驗投手控球和速度。它也是所有棒球愛好者必須了解的重要名詞。 (Zhíxiàn qiú (Straight Ball): The fundamental pitch in baseball, also the foundation for various other breaking pitches. When thrown, the ball travels rapidly towards the batter in a straight line, testing the pitcher’s control and speed. It is also an important term for all baseball enthusiasts to understand.)

* **Explanation:** This option emphasizes the importance and significance of the straight ball.

**Option 4 (Short and Sweet, Focusing on the Action):**

> 直線球 (Zhíxiàn qiú) : 棒球比賽中，快速筆直，直奔本壘板的投球！(Zhíxiàn qiú (Straight Ball): A fast, straight pitch heading straight for home plate in a baseball game!)

* **Explanation:** A more passionate and exciting description.

**To choose the best one for your WordPress setup:**

1. **Consider your audience:** Are they completely new to baseball, or already familiar?
2. **Think about the overall tone of your blog:** Are you aiming for a casual or more technical approach?
3. **Character limit:** Some WordPress themes have limits on the length of tag descriptions.

I recommend you use the translated English in the description if your target audience is both English and Chinese Speakers.

Good luck!