If you are making a bet or wager with someone, and you are both trying to guess as close to a particular value as you can (for example, date, weight or similar) then one particular strategy is to wait until the other person has guessed, and make your guess as close as possible to theirs, but, say, slightly above. This essentially guarantees that you will beat them if they have underguessed, and guarantees you will lose if they overguessed.
For example: My mother and I are trying to guess the date and time of when my sister will give birth, and whoever gets closest wins. I have guessed 8pm on a particular date, and my mother guessed 8.01pm on the same date.
I consider this frightfully unsportsmanlike, and I was wondering if there was a word/phrase to describe this sort of behaviour?