My Husband Has Type 2 Diabetes, Sometimes When He Comes

my husband has type 2 diabetes, sometimes when he comes In from tennis his blood sugar level is in the 150's this happened this morning when he in fact did not eat anything for breakfast, only coffee. His reading this am upon waking was 119, he did not inject his insulin and did not eat anything before 2 1/2 hrs. of tennis in Florida. We are wondering why. Can you give us an answer? Thank you