modified program

#include <NewPing.h>

#define LED_PIN    4
#define TRIGGER_PIN  12  // Arduino pin tied to trigger pin on the ultrasonic sensor.
#define ECHO_PIN     11  // Arduino pin tied to echo pin on the ultrasonic sensor.
#define MAX_DISTANCE 300 // Maximum distance we want to ping for (in centimeters).
NewPing sonar(TRIGGER_PIN, ECHO_PIN, MAX_DISTANCE); // NewPing setup of pins and maximum distance.
boolean trig = false;

void setup() {
  Serial.begin(115200); // Open serial monitor at 115200 baud to see ping results.
  pinMode(TRIGGER_PIN, OUTPUT); // don't forget to set all of your OUTPUT pins
  pinMode(LED_PIN,OUTPUT);
  digitalWrite(LED_PIN, LOW); // unless you are on a MEGA(?) pin 4 is likely to be digital only, no PWM. Without PWM you will have no analogWrite
//  analogWrite(LED_PIN,0);
  delay(1000);
}

void Engaged() {
  digitalWrite(LED_PIN,HIGH);
  Serial.println("This Hurt!!!");
}

void loop() {
  delay(50);                        // Wait 50ms between pings (about 20 pings/sec). 29ms should be the shortest delay between pings.
  unsigned int uS = sonar.ping(); // Send ping, get ping time in microseconds (uS).
  unsigned int distance = uS / US_ROUNDTRIP_CM;
  Serial.print("Ping: ");
//  Serial.print(uS / US_ROUNDTRIP_CM); // Convert ping time to distance in cm and print result (0 = outside set distance range)
  Serial.print(distance);
  Serial.println("cm");
//  if(trig == true) {
//    Engaged();
//  }
//  delay(50);
//  unsigned int uS = sonar.ping();
//  unsigned int distance = uS / US_ROUNDTRIP_CM;
  if(distance<10) {
    trig = true;
  } else {
//  delay(50);
//  if(distance>10) {
    trig = false;
    digitalWrite(LED_PIN,LOW);
  }
  if(trig == true) { // moved to respond after the distance has been checked
    Engaged();
  }
}