In the previous chapter, I recommended that you pursue Introduction to Data Science, a Coursera course by Bill Howe, Director of Research Scalable Data Analytics at the University of Washington. The seventh lecture of this course has two interesting videos on Overfitting, Evaluation, and Cross-validation. This is an introductory course and the videos are very intuitive.
Also, a very nice introductory book is Data Science for Business written by Foster Provost and Tom Fawcett, O'Reilly Media. This is a great book for a manager who needs to understand data science. The book has a nice chapter about overfitting and model evaluation.