Rib Fracture: The most likely diagnosis given the mechanism of injury (being tackled in a football game) and the location of the pain (right rib and RUQ area). Rib fractures are common in blunt trauma to the chest and can cause significant pain.

Muscle Strain: The force of being tackled could also result in strain to the intercostal muscles or abdominal muscles, leading to pain in the right rib and RUQ area.
Contusion: A bruise (contusion) to the chest or abdominal wall could also cause pain in the affected area.
Pneumothorax: Although less likely without other symptoms, a pneumothorax could occur due to the trauma and cause pain that might be referred to the right rib and RUQ area.

Hemorrhage or Internal Injury: Internal injuries such as a splenic rupture or liver laceration could present with RUQ pain and must be considered, especially if there are signs of shock or severe abdominal tenderness.
Pulmonary Embolism: Although rare in this context, a pulmonary embolism could cause sudden onset of chest pain and must be considered, especially if there are risk factors or other suggestive symptoms.
Cardiac Contusion or Myocardial Infarction: Direct trauma to the chest can cause cardiac contusion, and in rare cases, could precipitate a myocardial infarction, both of which are life-threatening conditions.

Diaphragmatic Rupture: A rare but serious condition where the diaphragm is torn, which could cause severe pain and respiratory distress.
Gallbladder Injury: Direct trauma to the gallbladder could cause injury, including rupture, which would be a rare but serious condition.
Pancreatic Injury: Although rare, pancreatic injuries can occur from blunt abdominal trauma and might present with abdominal pain, including in the RUQ area.