How to apply this function to the first row of a dataframe?

def calcScore(x,y):           
  if prem['FTHG'] > prem['FTAG']:
      x = 3
      y = 0
  elif prem['FTHG'] == prem['FTAG']:
      x = 1 
      y = 1
  else:
      x = 0
      y = 3

  return calcScore 

I have written this code but want to test it out on the first row of my dataframe, how would I do that?

I have tried many different ways but they just don't seem to work.