Depends on the location
Achilles tendon rupture
Calcaneal bursitis
Cellulitis
Compartment syndrome
Deep venous thrombosis (DVT)
Gastrocnemius strain
Ruptured popliteal cyst (Bakers cyst)<unk> 
Cellulitis
Deep venous thrombosis
Paget-Schroetter syndrome
Lymphatic obstruction
Necrotizing fasciitis<unk> 
SVC Syndrome
Thoracic outlet obstruction/Pancoast tumor
Paget-Schroetter syndrome
Athletic pubalgia
Cellulitis
Deep venous thrombosis
Hernia<unk>
Superficial thrombophlebitis
Depends on the location
Popliteal cyst
Achilles tendon rupture
Lymphangitis
Calcaneal bursitis
Portal vein thrombosis
Cellulitis