In contrast , the number of hours spent practicing defense during the primary season reaches 40 by age 10 and peaks at almost 90 by age 15 .
The number of defensive practice hours during the off - season never reaches 40 .
The number of hours spent practicing defense during the primary season reaches 40 by age 10 and peaks at almost 90 by age 15 .
The number of defensive practice hours during the off - season never reaches 40 .