It is a common thing to have red eyes after exercise. They should go back to normal soon and you don't need to worry. Strenuous exercise can cause increase in blood flow builds up pressure in your head, which results in blood vessels to expand, including those in your eyes. But there is the possibility that an underlying medical disorder, such as high blood pressure, could be the cause. Other common, less-worrisome causes include straining during exercise and irritants such as dust or sweat.
It is normal that getting red eyes after strenuous exercise. Certain form of exercise like lifting weights, require straining and cause momentary spikes in your heart rate that cause the blood flow building up pressure in your head. It will lead blood vessels to expand, Of course, including those in your eyes. If the pressure is too strong, the tiny blood vessels in your eye can burst that cause red eyes.