Why this script crashes Unity

You should post code using code tags ins$$anonymous$$d of posting an image.

the goto statement is what makes Unity crash since you are making an infinite loop. Like Landern mentions you should not use the goto statement.

$$anonymous$$aybe you can use this as inspiration to do what you want?

 using System.Collections;
 using UnityEngine;
 
 public class AsteroidSpawner : $$anonymous$$onoBehaviour
 {
     public GameObject largeAsteroid;
     public float initialSpawnTime = 10.0f;
     public float $$anonymous$$imumSpawnTime = 1.0f;
     public float spawnTimeDecrement = 1.0f;
     private float spawnTime;
     private Vector3 asteroidPosition;
 
     IEnumerator Start()
     {
         // Set initial spawntime
         spawnTime = initialSpawnTime + spawnTimeDecrement;
         // Wait 7 seconds before entering loop
         yield return new WaitForSeconds(7f);
         // Spawn the first Asteroid
         SpawnAsteroid();
         // Enter Infinite loop
         while (true)
         {
             var countdown = Time.time + spawnTime;
             while (countdown > Time.time)
             {
                 // Do nothing if Countdown is not finished
                 yield return null;
             }
             SpawnAsteroid();
             // Update countdown timer according to spawntime
             countdown = Time.time + spawnTime;
         }
     }
 
     void SpawnAsteroid()
     {
         float asteroidX;
         float asteroidY;
         if (RandomBool())
         {
             asteroidX = Random.Range(-11f, 11f);
             asteroidY = RandomBool() ? 5f : -5f;
         }
         else
         {
             asteroidY = Random.Range(-5.5f, 5.5f);
             asteroidX = RandomBool() ? 10f : -10f;
         }
         asteroidPosition = new Vector3(asteroidX, asteroidY, -1f);
         Instantiate(largeAsteroid, asteroidPosition, Quaternion.identity);
         DecreaseSpawnTime();
     }
 
     /// <summary>
     /// Decrease the spawntime by spawnTimeDecrement if more than $$anonymous$$imumSpawnTime
     /// </summary>
     void DecreaseSpawnTime()
     {
         // Do not decrease if spawnTime is less than $$anonymous$$imumSpawnTime;
         if (spawnTime < $$anonymous$$imumSpawnTime)
         {
             spawnTime = $$anonymous$$imumSpawnTime;
         }
         else if (spawnTime > $$anonymous$$imumSpawnTime)
         {
             spawnTime -= spawnTimeDecrement;
         }
     }
 
     /// <summary>
     /// Returns a random Bool
     /// </summary>
     /// <returns></returns>
     bool RandomBool()
     {
         var random = Random.value > 0.5f ? true : false;
         return random;
     }
 }