private int[] activeFielderNumber = new int[10];
private string[] activeFielderAction = new string[10];
....
...
....
Array.Clear(activeFielderNumber, 0, activeFielderNumber.Length);
Array.Clear(activeFielderAction, "", activeFielderAction.Length);

error CS0103: The name `Array' does not exist in the current context

using System;

Array.Clear(activeFielderAction, "", activeFielderAction.Length);

Array.Clear(activeFielderAction, 0, activeFielderAction.Length);

using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] activeFielderNumber = new int[10];
string[] activeFielderAction = new string[10];

Array.Clear(activeFielderNumber, 0, activeFielderNumber.Length);
Array.Clear(activeFielderAction, 0, activeFielderAction.Length);
        }
    }
}

Array.Clear(activeFielderAction, "", activeFielderAction.Length);

int[] activeFielderNumber = new int[10];
activeFielderNumber[1] = 10;
activeFielderNumber[2] = 20;

string[] activeFielderAction = new string[10];
Array.Clear(activeFielderNumber, 0, activeFielderNumber.Length);
Array.Clear(activeFielderAction, 0, activeFielderAction.Length);

for (int x = 0; x < MAX; x++)
{
    o1[x] = null;
}

Array.Clear(o1, 0, o1.Length);

Parallel.For(0, MAX, x =>
{   //arrays are thread safe if only one thread is writing to an index
    o1[x] = null;
});