https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3249911/

Free Radicals are generated from inside and outside:

From normal resporation & metabolic processes;

From the "bad ozone" in the air we breathe; 

From cigarette smoking, alcohol & medications;

From whats in the foods we eat;

From pollutants like industrial chemicals & toxic herbicides, pesticides;

and the list goes on and on ...

Some Key Article Takeaways:

"Targets of free radicals include all kinds of molecules in the body [molecules operate inside cells]. Among them, lipids, nucleic acids, and proteins are the major targets."

So adding Sporting Activities or Exercise creates an even greater load that further increases free radicals that should be redressed post-activities. 

"Free radical reactions are expected to produce progressive adverse changes that accumulate with age throughout the body";

Genetic predispositions also plays a role in how oxidative stresses impact from individual to individual. 

Cancer and Heart Disease (clogged arteries) are the two major causes of death, they are "salient free radical diseases" that creep up over time.

WHAT CAN HELP TILT THE SCALES BACK IN BALACE:

"Antioxidants like B-carotene or vitamin E play a vital role in the prevention of various cardiovascular diseases."

"Antioxidants can safely interact with free radicals and terminate the chain reaction before vital molecules are damaged. Some of such antioxidants, including GLUTATHIONE, ubiquinol, and uric acid, are produced during normal metabolism in the body."

"Reduction of free radicals or decreasing their rate of production may delay aging. Some of the nutritional antioxidants will retard the aging process and prevent disease."

"The principle micronutrient (vitamins) antioxidants are vitamin E (α-tocopherol), vitamin C (ascorbic acid), and B-carotene.[32] The body cannot manufacture these micronutrients, so they must be supplied in the diet."

"In cells, VITAMIN C is maintained in its reduced form by reaction with GLUTATHIONE."

"The identification of vitamins A, C, and E as antioxidants that revolutionized the field and led to the realization of the importance of antioxidants in the biochemistry of living organisms."

"Strong antioxidants activities have been found in berries, cherries, citrus, prunes, and olives."

"The major active nutraceutical ingredients in plants are flavonoids. As is typical for phenolic compounds, they can act as potent antioxidants and metal chelators."