Trauma: This is the most common cause of leg bruising and pain, resulting from direct injury to the leg, such as a fall or a blow. The mechanism of injury can lead to blood vessel damage, causing bruising, and soft tissue injury, leading to pain.

Deep Vein Thrombosis (DVT): DVT can cause leg pain and swelling, and sometimes bruising, especially if the clot is large or has caused significant inflammation. Risk factors include recent surgery, immobilization, cancer, and genetic predispositions.
Varicose Veins: Varicose veins can lead to chronic venous insufficiency, causing pain, swelling, and bruising in the legs due to poor blood circulation.
Muscle Strain: Overuse or direct injury to the muscles in the leg can cause strain, leading to pain and bruising.
Insect Bites or Stings: Certain insect bites or stings can cause localized bruising and pain.

Pulmonary Embolism (if DVT is suspected): While not directly causing bruising, if DVT is suspected, it's crucial to consider the risk of pulmonary embolism, a potentially life-threatening condition where the clot breaks loose and travels to the lungs.
Cellulitis: A bacterial infection of the skin and soft tissues that can cause pain, redness, swelling, and sometimes bruising. It requires prompt antibiotic treatment to prevent serious complications.
Osteomyelitis: An infection of the bone that can cause pain and, less commonly, bruising. It's a serious condition that requires early diagnosis and treatment.

Hemophilia: A genetic disorder that impairs the body's ability to make blood clots, a process needed to stop bleeding. It can lead to spontaneous bruising and bleeding into joints and muscles.
Vasculitis: Inflammation of the blood vessels that can cause a variety of symptoms, including bruising and pain, depending on the vessels affected.
Sickle Cell Disease: A genetic disorder that affects hemoglobin production, leading to abnormal red blood cells. These cells can get stuck in small blood vessels, causing pain episodes and potentially bruising.
Antiphospholipid Syndrome: An autoimmune disorder that increases the risk of blood clots, which can cause leg pain and bruising if clots form in the legs.