You should worry about leg pain and seek medical attention or emergency care in the following situations:

• If you have leg pain accompanied by swelling, redness, warmth, or tenderness, which could indicate a blood clot or infection.
• If pain is severe and makes it difficult to walk or put weight on the leg.
• If you have signs of infection such as fever over 100°F (37.8°C).
• If you experience sudden worsening of symptoms or develop symptoms without a clear cause.
• If you notice a leg that is pale, cool, numb, weak, or deformed.
• If you have calf pain after prolonged sitting (like a long car or plane ride).
• If the leg pain occurs with swelling in both legs plus breathing problems.
• If there is a serious injury with exposed bone or tendon, or if you hear popping or grinding sounds in the leg.
• If leg cramps last longer than 10 minutes or become unbearably painful.
• If leg pain happens regularly during exercise and improves only with rest, possibly indicating peripheral artery disease (PAD).

Minor muscle aches after exercise that improve with rest are usually not concerning, but unusual or persistent pain that worsens or is accompanied by any of the above signs should be evaluated promptly by a healthcare provider or in an emergency setting, depending on severity.

In summary, immediate medical help is needed for signs of blood clots, infections, severe injuries, or sudden worsening symptoms. Otherwise, seek timely medical advice if pain persists, worsens, or is associated with other concerning symptoms.