7.3 Odds Movements inplay the game
The basic rule to predict how the odds move during the game is to predict the time of next goal.
When a football game starts and the elapsed time goes on possibilities of current and next scores change every minute.
Eg. When the score remains 00
At Elapsed 5min probability for 00 is 12%
At Elapsed 20min probability for 00 is different 18%
In order to understand odds movements of the odds we divide football game in two period.

Before the First Goal

After the First Goal
Before the First Goal
When the football game is inplay and there is still no goal, some markets reduce the odds and some others increase the odds.
For example as the elapsed time goes on Under goal markets, Draw, no goal markets etc are more possible to succeed as the elapsed goes on without a goal, so their odds reduces.
For Over goal markets, both teams to score markets etc, as the elapsed goes on without a goal their odds increased.
According to a very popular article “The science of Betfair Graphs” if we analyses the behavior of Under 2.5 market there is an idealized behavior of price movements. The fundamental law of an Under goal graph during a match with no goals scored is reduction of prices (odds), as the possibility of the event to happened increase.
Figure 1 below shows the above behaviour. When there is no scoring in the match the possibility of Under 2.5 market increase as it shown in the .
At the same time there is a reduction of the odds.
Figure 1: Idealized Behavior of Under goal market based on Betfair Exchange graphs
The idealized behaviour of odds movement as it shown in figure 1 starts from a value n0 when the football match begin and follow a smooth curve 1 until t0 time.
Between t0 & tE time the inclination of the curve 2 are steeper than curve 1 and after tE close to the end of the game the curve is getting smoother (curve 3).
The explanation of this behavior is:
Curve 1:
From the beginning of the match until t1 time, which is usually t0=1012min, the possibility of the event to occur does not change dramatically, because it is a very short time of the game and the two teams usually do not attack enough.
Nevertheless, it is very interesting to learn that at the first 10min of a football match, there is a big possibility of scoring.
Curve 2:
The inclination of this curve is definitely steeper than the inclination of curve 1. This curve represents the main part of the match, from time t0=1012min until tE=7085min. As there is no goal during the match the possibility of the event (Under 2.5 or 1.5 etc) to occur increases and because of that the odd prices reduce.
Having in mind that curve 2 represented the idealized behaviour of average price movements. In real Betfair graphs curve 2 include many fluctuations or parts with different inclinations. About turning points the exact values of time t0 and tE are different among markets Under 1.5, Under 2.5, Under 3.5 and Under 4.5 and depends of the type of the match. A generalized rule is that value of t0 is close to 10min and tE ranges between 70 to 85min.
Curve 3:
Represents the price movements for the last minutes of the match. At that time and because no goal were scored, the possibility of the event to occur (Under 2.5 etc) is already high. The odds price is already small (value ntE) and because of that the inclination of specific curve is smooth and until the end of the game.
Definition of Price Rate of Movement
Trying to understand Betfair graphs is very useful to define the Rate of price movements.
In figure 4.2 there is a typical section of a Betfair odds graph showing the inclination of the curve. To define the inclination of the curve we have to measure the number of ticks the price reduced in one minute. So the definition of the Rate is:
r= (tick reduction) / minute
Example 1:
At time t=10min the odd for Under 2.5 is n=1.80
At time t=11min the odd for Under 2.5 is n=1.78
The rate r of the curve is:
Price reduction (1.801.78)=0.02 that means 2 ticks (because between odds 1.012.00, one tick=0.01)
Time difference is 1110=1min.
So r=2/1 that means r=2 tick/min
After the First Goal
Figure 2 shown a typical idealized graph of a football match with two goals scored. Let’s have a look at the graph:
• Time t0
Until time t0 the curve has a small rate r0 of odd reduction, close to the start of the game.
• Time t0 to tG1
After t0 curve is being steeper with rate r1 as it has been explained in previous paragraphs. At time tG1 a goal is scored and because the possibility of the event for etc Under 2.5 reduced, there is a sharp and perpendicular increase of the odd price. From now on we call this price movement as peak.
• Time tG1 to tG2
After the goal there is a period of time that the rate rG1 of the curve is steady to smooth, because many people sell and buy bets. After that period curve with rate rG1a is becoming quick and usually steeper than curve with rate r1. When the second goal comes at time tG2 another peak moves the price at high values.
• Time tG2 to End of the Game
After the second goal there is a period of time that the rate rG2 of the curve is steady to smooth. If, for example, you are in Under 2.5 market this period will be stayed a lot of minutes, more than the correspondence period of the first goal, because with an another third goal market is closed.
After that period curve with rate rG2a is becoming quick and sometimes sharp, usually steeper than curve with rate rG1a.
Figure 2: Idealized Behavior of Under goal market with two goals scored.