Begging is an action that participants can take with the Bread Crumbs snack when they have 0 or less coins. When they do so, the Blaseball Gods grant them coins so that they may continue gambling, in a random quantity between approximately 5-20.
A player can beg if they have 0 or less coins, and since the introduction of Concessions, has required the Bread Crumbs snack to access. Before Season 12, a player with negative coins was not able to beg. 
It is widely considered optimal for players to bet until they have 0 coins, then beg, then bet, then beg, and so on until all active games have bets placed: this maximizes the total of coins earned, even in small increments.
The number of begs is viewable on a player's Account page. It is unknown whether begging has long-term consequences.
The remainder of this article contains lore created collaboratively by the Blaseball community.
There has been no conclusive study as to what factors affect the number of coins gifted by the gods. However, some players recite short poems as they bet, believing it to raise the average number of coins when recited with sufficient passion. Some players create their own poems. Fans of the Breckenridge Jazz Hands often sing them.
Here is one example of such a traditional Blaseball poem. (Author unknown.)
In the splort that will take place,
Let us fill up ev'ry blase.
And if this wish you'll refuse,
May I have some coin to lose!
Several organizations of participants & fans believe that begging itself is an act of dependence and worship that serves to make the Blaseball Gods more powerful.
"By succumbing our bodies to the act of panhandling, we likewise capitulate our souls to the state of dependency. If the Gods are to dictate our very fortunes — if they are to throw our games or cast into the void our hard earned wealth, only for us to come crawling back on hands and knees and entitled brows, asking for their favor yet again, day after seasonal day — then the control that the Gods have over our fate is immeasurable. I fear what they say is absolutely true: the Gods cannot be killed."
- u/stickysandals (30 Jul 2020). "I have -7 coins. Can't even beg the gods." (Post) - via Reddit.