Golf League Tracker requires that you enter all hole scores for each player (or mark the player as absent) to complete a scorecard. If a player has an incomplete round because of a rainout or some other circumstance, it is suggested you follow the USGA process when a round is incomplete.
How your league handles incomplete rounds is up to you, and it is suggested that you have hard and fast rules that are written down so there is no controversy going forward. My league follows the USGA rules for incomplete rounds, but we also have a rule which states that at least 6 holes must be played by ALL PLAYERS (out of the 9) for the week to count, otherwise all scores are discarded.
While most incomplete rounds are due to weather, some are for other reasons. For weather, there has to be a dangerous situation or the course is unplayable for players to quit without getting penalized. If someone quits just because it's "too rainy" or "too cold", they lose the remainder of the holes.
We also differentiate for illness or injury. The player will not be penalized in those circumstances, and their holes will be completed per the USGA process outlined in this document.