```ruby
module SportsSouth
  # Holds methods common to all classes.
  class Base

    protected

    def requires!(hash, *params)
      params.each do |param|
        if param.is_a?(Array)
          raise ArgumentError.new("Missing required parameter: #{param.first}") unless hash.has_key?(param.first)

          valid_options = param[1..-1]
          raise ArgumentError.new("Parameter: #{param.first} must be one of: #{valid_options.join(', ')}") unless valid_options.include?(hash[param.first])
        else
          raise ArgumentError.new("Missing required parameter: #{param}") unless hash.has_key?(param)
        end
      end
    end

  end
end
```

Refactor Base.requires! so it can be used as a class or instance method.
user
```ruby
module SportsSouth
  # Holds methods common to all classes.
  class Base

    protected

    # Wrapper to `self.requires!` that can be used as an instance method.
    def requires!(*args)
      self.class.requires!(*args)
    end

    def self.requires!(hash, *params)
      params.each do |param|
        if param.is_a?(Array)
          raise ArgumentError.new("Missing required parameter: #{param.first}") unless hash.has_key?(param.first)

          valid_options = param[1..-1]
          raise ArgumentError.new("Parameter: #{param.first} must be one of: #{valid_options.join(', ')}") unless valid_options.include?(hash[param.first])
        else
          raise ArgumentError.new("Missing required parameter: #{param}") unless hash.has_key?(param)
        end
      end
    end

  end
end
```
assistant