Using OnTriggerEnter to change UI text - unity3d

Question

Hey so I'm building a baseball game and I'm using OnTriggerEnter to detect whether or not the baseball enters the strike zone. The strike zone is big enough so it can be detected and the ball isn't moving too fast. I want to display ("STRIKE!) once it hits the trigger, but nothing is happening. pls
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
public class Strike : MonoBehaviour {
public AudioSource src;
public ParticleSystem stars;
public Text StrikeText;
private void Start()
{
StrikeText.text = " ";
}
public void OnTriggerEnter(Collider other)
{
if (other.gameObject.tag == "ball")
{
src.Play();
Instantiate(stars, transform.position, transform.rotation);
StrikeText.text = "STRIKE!";
Destroy(other.gameObject);
SecondsWait();
StrikeText.text = " ";
}
}
IEnumerator SecondsWait()
{
yield return new WaitForSeconds(4);
}

Answer 1

That's not how coroutines work.
This is what your code is doing, line by line:
src.Play();
Instantiate(stars, transform.position, transform.rotation);
StrikeText.text = "STRIKE!";
Destroy(other.gameObject);
All of that runs as normal, just as you expect/want
SecondsWait();
This invokes a function that then invokes yield return new WaitForSeconds(4); As your code doesn't do anything with this return value, nothing happens, and the WaitForSeconds object gets garbage collected.
StrikeText.text = " ";
Then this line runs immediately, clearing out the text you'd previously set.
This is what you probably actually want:
src.Play();
Instantiate(stars, transform.position, transform.rotation);
Destroy(other.gameObject);
StartCoroutine(SecondsWait());
//...
IEnumerator SecondsWait()
{
StrikeText.text = "STRIKE!";
yield return new WaitForSeconds(4);
StrikeText.text = "";
}
By calling StartCoroutine() and passing the return of SecondsWait() to it, the SecondsWait() method itself (not OnTriggerEnter!) pauses when the yield occurs.

Answer 2

By the way this kind of code architecture is very poor. UI should never be related directly on your domain. You should consider using event-driven approach, even if you are just a very beginner.