Is an underarm serve really that effective for Nick Kyrgios? Maths professor finally reveals the truth - Tennishead
What's Wrong With an Underhand Serve in Tennis?
Why do tennis players underarm serve, is it legal and what did they say? Nick Kyrgios and Andy Murray explain shot | The US Sun
This trio of women's tennis players uses underhand serves to their advantage | The Daily Pennsylvanian
Underhand Tennis Serve: Rules with Serving Underhand | USTA.com
Nick Kyrgios Underarm Serve Compilation | "Nick Kyrgios and the underarm serve" One of tennis' most talked-about stories over the past year... | By Tennis TV | Facebook